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1908
South 180th Street Grade Separation
Final Design Report
Volume 1 of 2 - Text and Appendices
Submitted to
City of Tukwila
Public Works Department
Tukwila, Washington
Submitted by
BERGER/AB"
E N G I N E E R S I N C.
Job No. A99002 August 1999
SOUTH 180TH STREET GRADE SEPARATION
FINAL DESIGN REPORT
Volume 1 of 2 — Text and Appendices
Submitted to
City of Tukwila
Department of Public Works
Tukwila, Washington
August 1999
Submitted by
BERGERIABAM Engineers Inc.
33301 Ninth Avenue South, Suite 300
Federal Way, Washington 98003-2600
Job No.A99002
SOUTH 180TH STREET GRADE SEPARATION
FINAL DESIGN REPORT
VOLUME 1 OF 2-TEXT AND APPENDICES
TABLE OF CONTENTS
SECTION PAGE
1.0 Executive Summary .....................................»................................................................ iv
1.1 Introduction ........................................................................................................ iv
1.2 Grade separation Options ................................................................................ iv
1.3 Environmental Considerations ...................................................................... vi
1.4 Detours
1.5 Project Costs
1.6 Additional Alternatives
2.0 Introduction and Existing Conditions ....................................................................... 1
2.1 Introduction ........................................................................................................ 1
2.2 Scope of Work ..................................................................................................... 1
2.3 Existing Conditions ........................................................................................... 1
3.0 Roadway Improvements ................................................................................................ 3
3.1 Design Parameters and Standards ................................................................ 3
3.2 Traffic Analysis .................................................................................................. 3
3.3 Roadway Section ................................................................................................ 4
3.4 Roadway Alignment .......................................................................................... 4
3.5 Bike Lanes ........................................................................................................... 5
3.6 Pedestrian Amenities ........................................................................................ 5
3.7 Intersections ....................................................................................................... 5
3.8 Access and Driveways ....................................................................................... 5
3.9 Tremie Seal .......................................................................................................... 6
3.10 Drainage ............................................................................................................... 7
3.11 Utilities ................................................................................................................. 8
3.12 Retaining Walls .................................................................................................. 10
3.13 Secant Pile and Pier Facade ........................................................................... 11
3.14 Right-of-Way/Easements .................................................................................. 11
3.15 Springbrook Creek Culvert Replacement ................................................... 12
4.0 Bridges ............................................................................................................................... 13
4.1 Introduction ........................................................................................................ 13
4.2 Interurban Trail Bridge ................................................................................... 14
4.3 Railroad and Access Road Bridges................................................................. 16
4.4 Railroad Shoofly and Track Realignment ................................................... 23
SOUTH 180TH STREET GRADE SEPARATION
FINAL DESIGN REPORT
VOLUME 1 OF 2—TEXT AND APPENDICES
TABLE OF CONTENTS
(continued)
5.0 Project Aesthetics ........................................................................................................... 25
5.1 Landscaping ........................................................................................................ 25
5.2 Architectural Treatments ................................................................................ 25
5.3 Illumination ......................................................................................................... 25
6.0 Traffic Control ................................................................................................................. 26
6.1 Detours ................................................................................................................. 26
6.2 Access During Construction ............................................................................ 26
7.0 Schedule ............................................................................................................................ 27
7.1 Project Schedule ................................................................................................ 27
7.2 Construction Schedule ..................................................................................... 27
8.0 Environmental Considerations ................................................................................... 29
8.1 Streams ................................................................................................................. 29
8.2 Wetlands ............................................................................................................... - 29
8.3 Wildlife .................................................................................................................. 31
8.4 Water Quality ...................................................................................................... 32
9.0 Project Costs .................................................................................................................... 34
10.0 Public Involvement ........................................................................................................ 35
11.0 Endorsement .................................................................................................................... 38
APPENDICES
A Preliminary Cost Estimates
1.0 EXECUTIVE SUMMARY
1.1 INTRODUCTION
The City of Tukwila is initiating a grade separation on South 180th Street between vehicular traffic
and railroad tracks owned by Burlington Northern Santa Fe(BNSF)and Union Pacific(UPRR). See
Figure 1 in Volume 2 of this report for a vicinity map. The corridor is classified as a principal
arterial facilitating east-west vehicular traffic in the Tukwila,Renton, and Kent areas of the Green
River Valley. The existing four-lane roadway serves not only local connections between SR 181
(West Valley Highway) and East Valley Highway,it is also part of a central corridor feeding State
Route 167 (SR 167). Currently, South 180th Street is the only major crossing of the railroads for 3.5
miles between Interstate 405 (I-405)and South 212th Street. As a result,the existing roadway
experiences high traffic volumes. The existing north-south rail corridor currently contains three sets
of tracks,two BNSF and one UPRR. These lines are heavily used for both freight and passenger
service,with upwards of 60 trains per day. The intersection of these two heavily used corridors
results in not only extensive traffic delays but also in numerous accidents. From 1996 through 1998,
24 accidents were reported on South 180th Street. One of the accidents in 1998 resulted in two
fatalities when a train hit a car. In addition, the Interurban Trail crosses South 180th Street just
west of the UPRR tracks. The trail is widely used as a walking and bicycle path.
A regional program, Freight Mobility Strategic Investment Board(FMSIB),has been established to
help fund the design and construction of grade separations. The main objective of the program is to
provide safe and efficient roadways and railroads. In response to the obvious safety issue, the City of
Tukwila applied for and received funding for the separation on South 180th Street and the railroad
tracks. The project budget has been established at $15.0 million with the FMSIB, the cities of
Tukwila and Renton, the Port of Seattle, King County,Washington State Department of
Transportation (WSDOT), and both railroads contributing a portion.
A technical advisory committee (TAC)was formed to oversee the development of the preliminary
design of the project because of its importance to regional transportation. Representatives from the
cities of Tukwila, Renton, and Kent; WSDOT; King County; and BNSF and UPRR comprise the
committee. Several meetings have been held over the past year to gain input and support from all
stakeholders in the project.
This report is the culmination of the preliminary design and evaluation of this project. Upon
acceptance of the findings,the design will progress to Phase II. At that time a complete plans,
specifications, and cost estimate (PS&E) package will be produced for construction.
1.2 GRADE SEPARATION OPTIONS
In studying alternatives to meet the project's goals, four main issues were evaluated. They included
the number of lanes for the new roadway, method of separation (vertical alignment—pass under or
over the existing tracks), maintaining traffic during construction, and meeting overall project
budget. Refer to Figures 2 to 7 for corresponding graphical depictions of the following descriptions.
Number of Lanes
A thorough comparison and analysis was conducted between maintaining four lanes and increasing
the roadwav width to accommodate six lanes. Listed below is a summary of the findings for the
selection of a four-lane roadway as the preferred alternative.
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South 180th Street Grade Separation iv August 1999
Four-Lane Alternative
■ Meets the goals of the project; safe and efficient travel within 5 percent of the established project
budget.
■ The grade separation eliminates traffic delays due to train crossings.
■ The Draft Traffic Analysis report shows only minimal difference in the year 2020 corridor level of
service between the four-lane and six-lane options. The report also indicates that an additional
east-west connection between SR 181 and East Valley Highway is necessary to meet future
traffic volume projections for either a four-lane or six-lane alternative.
■ Regardless of the number of lanes constructed in this project,the intersections at SR 181 and
Oaksdale Avenue will ultimately control the level of service.
■ Reduced limit of work requires only minor reconstruction of one intersection, 72nd Avenue
South.
Six-Lane Alternative
■ The project budget is exceeded with the addition of lanes. Another lane in each direction would
result in a 30 percent increase in the area of the bridges required for either the overpass or
underpass option.
■ An additional arterial crossing is still necessary to meet future traffic volumes (2020).
■ The project limits are approximately 1,400 feet longer,extending from West Valley Highway to
80th Avenue South. The result is more impacts to adjacent properties and additional right-of-
way(ROW)takings.
Over Versus Under
An extensive investigation was conducted between the two grade separation alternatives; passing
over or going under the tracks. Two distinct overpass options were explored; an all-bridge
alternative, and a combination of bridge and embankment with retaining wall alternative. See
Figures 3 and 4 for plan and profile of these options. Listed below is a summary of the findings
leading to the underpass being the preferred method of separation.
Going Over the Railroads
■ An overpass will greatly exceed the project budget. Depending upon the overpass option used,
the four-lane overpass is 30 to 80 percent more expensive than an underpass.
■ The overpass will result in considerable additional ROW impacts as compared to the underpass
option. Specifically, Building Nos. 7210, 7220, (see Figure 12)and the new Public Storage
facility southeast of the track/road intersection would probably be acquired or significantly
altered if this option were chosen. If these commercial facilities were to remain, they would face
a 7- to 10-foot retaining wall. Also, these properties would lose their most valuable asset, direct
access from South 180th Street.
• An existing high-voltage power line owned by Puget Sound Energy(PSE)passes over the
corridor just east of the Interurban Trail. This utility currently has ownership,not easement
rights to the property on which it's located. And as such, any costs associated with the relocation
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South 180th Street Grade Separation v August 1999
of this utility will be incorporated in this project. Maintaining adequate clearance would require
the existing aerial power lines to be raised if a roadway overpass is constructed. This work has
been estimated at$2 million.
■ The project limits will extend from West Valley Highway to beyond the Springbrook Creek
Crossing.
■ As compared to the underpass,the overpass bridge would produce a significant visual impact to
the area.
■ The overpass will not require a temporary railroad detour(shoofly). This would minimize
impacts to the railroads and greatly reduce the coordination with UPRR and BNSF necessary
during construction.
Going Under the Railroads
■ Construction costs are within 5 percent of the established project budget.
■ The underpass will have significantly less ROW impacts to adjacent properties.
■ Currently, the existing roadway ramps upward at approximately 6 percent as it approaches the
tracks resulting in a substantial(5-to 8-foot)grade difference. This profile is more conducive for
an underpass rather than an overpass. The fact that the railroads are this much higher than the
existing ground benefits the underpass option in that the clearance requirement of 16.5 feet
necessitates only 24 feet of cut. See Section 4.3.1 for geometric requirements for railroad and
access road bridges.
■ The roadway reconstruction limits are reduced by approximately 500 feet.
■ The underpass alternative requires the construction of a shoofly. While the construction costs
for the shooflies are significant, it is more than offset by the additional costs of the overpass as
described above. A discussion of the shoofly follows in Sections 1.4 and 7.
■ No impacts to Springbrook Creek will result from the underpass. However,impacts to the
wetlands along the railroad ROW due to the shoofly will require permits and mitigation.
1.3 ENVIRONMENTAL CONSIDERATIONS
Environmental considerations within the study area include wetlands, streams, and wildlife habitat.
Mill and Springbrook creeks and six wetlands occur within the project area. Impacts to Mill Creek
will occur as a result of temporarily widening the BNSF bridge over the creek. The temporary bridge
area of disturbance will be approximately 90 feet long by 30 feet wide. No in-stream work below the
ordinary high-water mark is proposed. Small pilings will be driven into the streambank within the
50-foot stream buffer to support the bridge deck.
Approximately 1.1 acres of wetlands within the study area boundaries will be filled, and
approximately 2.3 acres of wetland buffer will be impacted as a result of the development of four
shooflies for the BNSF and UPRR tracks.
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South 180th Street Grade Separation vi August 1999
1.4 DETOURS
Roadway
South 180th Street is a critical east west connector in the valley. Currently, South 180th Street is
the only major crossing of the railroads for 3.5 miles between I-405 and South 212th Street. The
project must maintain or provide alternatives for through traffic for the duration of construction.
One option to accomplish this is to construct extensive temporary detour(s). See Figures 5 and 6 for
underpass and overpass detour alternatives. Upon review of these detour layouts,it was determined
that it is more beneficial to the project to not construct a detour around the project site. Rather,the
traffic will be routed to South 196th Street. The findings associated with the two options are listed
below. See Section 6.1 for additional discussion.
Temporary South 180th Street Detour
■ The construction of these detours would result in significant added costs that would exceed the
project budget.
■ The delays associated with the construction work adjacent to the detour would result in backups
stretching into the intersections.
■ The temporary detours will result in environmental impacts above and beyond those associated
with the project itself. Specifically, the Springbrook Creek Culvert would have to be extended
and adjacent wetlands would be impacted.
■ These detours would require temporary at-grade intersections with the railroads. This will not
only perpetuate an already dangerous crossing situation, it will likely increase the danger due to
the presence of large construction equipment.
■ Allows for construction to begin in 2000 with a construction schedule estimated at 18 months.
Using South 196th Street
■ The detour requirements are minimal; temporary signing and barricades. This will add minimal
expense and provide opportunities to save the project budget.
■ The property and environmental impacts will be minimized to those due solely to reconstruction
of the South 180th Street and not the temporary detours.
■ Using South 196th Street as the detour removes all South 180th Street at-grade railroad
crossings as soon as South 180th Street is closed.
■ Construction of South 180th Street in early 2001 with an estimated construction schedule of
approximately nine months. Using South 196th Street will require construction to be delayed
approximately one year. However, the net effect is only a three- to four-month delay because of a
shortened construction schedule.
Railroad
To create a safe work zone for construction of the railroad bridges, a shoofly for each railroad track
must be constructed. Figures 7 to 10 show the proposed railroad shooflies and construction
sequence. First, as shown in Figure 7, three BNSF shoofly tracks will be constructed west of the
existing tracks. BNSF rail traffic will be diverted onto these tracks and the BNSF bridge will be
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South 180th Street Grade Separation vii August 1999
constructed. Upon its completion,the tracks will be re-established on the new bridge(Figure 8).
Next,the UPRR shoofly will be constructed and UPRR traffic diverted onto it so the UPRR bridge
can be constructed(Figure 9). Once completed,the UPRR tracks will be reestablished on the new
bridge. After the railroad bridges are in operation,the shared access road bridge can be constructed.
1.5 PROJECT COSTS
Aside from safety,the overriding factor for this project is cost. With a strict budget of$15 million,it
was important to combine the various design elements so that the project goal can be met while
staying within budget. Included in Appendix A is a detailed construction cost analysis of the options
described above.
With an estimated cost of$15 million,the preferred alternative, a four-lane underpass,is
considerably less expensive than the other options, and is within 5 percent of the established project
budget.
1.6 ADDITIONAL ALTERNATIVES
In discussion with the BNSF and UPRR it was learned that both companies are planning for future
additional tracks along the project corridor. This would of course result in larger and more
expensive bridges. The preferred alternative will be used as a baseline for comparison purposes.
Add-on alternatives include a four-track BNSF bridge, a two-track UPRR bridge, and an access road
bridge. A"suboption"to these alternatives is to construct only the foundation for these bridges. This
will allow for the superstructure to be constructed at a later date. Section 4 outlines the various
alternatives and the corresponding cost increases presented in Section 9.0. If additional funds can
be procured, it is likely that these alternatives will be constructed as part of this project.
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South 180th Street Grade Separation viii August 1999
2.0 INTRODUCTION AND EXISTING CONDITIONS
2.1 INTRODUCTION
This design report is the culmination of all the engineering and data gathering efforts to date by the
design team for the City of Tukwila's South 180th Street grade separation project. The proposed
design as described in the following sections is based upon a detailed evaluation of several
alternatives. The preferred design option is as follows.
■ The proposed roadway will maintain four lanes. A center left turn or median lane will also be
included to accommodate left turns and the center bridge pier.
■ The right lane will be widened to 15 feet to better accommodate bicycles.
■ The new roadway will be realigned under the existing railroad tracks.
■ Bridges will be constructed for the BNSF(two tracks),UPRR(one track), and the Interurban
Trail.
■ Replacement or relocation of several utilities will be required.
2.2 SCOPE OF WORK
BERGER/ABAM Engineers Inc. was retained to lead a design team responsible for the roadway, rail,
and bridge design and specific environmental assessments for the South 180th Street grade
separation project. This design report and accompanying preliminary design will conclude Phase 1
of the project. Upon acceptance of this report, Phase 2 will commence. Phase 2 will entail
preparation of final PS&E for construction. Phase 3 will be the construction administration services
for the project.
2.3 EXISTING CONDITIONS
2.3.1 Roadway
South 180th Street from SR 181(West Valley Highway)to 80th Avenue South (Oaksdale Avenue)
varies from four to five lanes and has signalized intersections at both ends of the corridor and at
72nd Avenue South. The roadway is posted for 35 mph and consists of two 10-to 12-foot-wide
through lanes in each direction with left-turn (or center-turn)lanes at each intersection. There are
minimal to nonexistent shoulders. A curbed 6-foot concrete sidewalk runs along both sides of the
road for most of the corridor. At the railroad crossing area, there is a wide paved shoulder that
serves pedestrian crossing of the tracks.
2.3.2 Utilities
There are numerous major public and private utilities along and crossing the corridor.
■ Two distinct drainage systems, one on each side of the railroad tracks, are present. On the west
side, the runoff collected along South 180th Street is conveyed off site via a 12-inch trunk line on
72nd Avenue South. East of the tracks, all stormwater runoff is collected in a series of basins
and eventually discharged to Springbrook Creek via a 36-inch outlet.
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South 180th Street Grade Separation 1 August 1999
■ As with the drainage,there are separate sanitary sewer systems on each side of the tracks. Both
systems are owned and maintained by the City of Renton. On the west side,the system directs
flows from the west to a manhole in the center of the roadway just west of the Interurban Trail.
From there,the system flows north along the western edge on the trail. East of the tracks, the
system begins at the Public Storage facility and flows east towards Oaksdale Avenue.
■ A 12-inch water main runs for the length of the corridor under South 180th Street supplying
water to the businesses and residences along the corridor. This main is owned and maintained
by the City of Renton and is a primary feed for Tukwila in this area.
■ Existing high-voltage power lines owned by PSE pass over the corridor just east of the
Interurban Trail. Also,there are several power vaults and buried lines along the corridor
supplying individual services to adjacent properties and roadway lighting.
■ PSE also owns and maintains a 16-inch gas main under South 180th Street.
■ Located between and running parallel to the existing rail lines are several fiber optic
telecommunication lines that cross the roadway. The lines are owned by MCI World Com,
AT&T, and Sprint.
■ US West provides phone service throughout the corridor with buried phone lines.
■ A jet fuel supply line crosses under the roadway just west of the Interurban Trail. This 14 inch
fuel line is owned and operated by Olympic Pipeline, Inc.
2.3.3 Adjacent Properties
With the recent completion of the Public Storage facility and the ongoing commercial/industrial
construction along the northeast quadrant of the project, all nonwetland/open space properties
adjacent to the corridor have been developed. However,the usage is quite varied. West of the tracks
there is commercial, retail, and even residential properties. The east side of the project contains
commercial and office buildings.
Several owners on the west side have expressed a desire that their property not be purchased as part
of this project. Even without a direct access to South 180th Street, the owner of Building No. 7220
has requested that the proposed roadway be designed to allow for future use of this structure. The
owners of Building Nos. 7209 and 7211 made the same request. The location of these buildings are
shown in Figure 12.
2.3.4 Streams and Wetlands
Two waterways, Springbrook Creek and Mill Creek, and several wetlands are located within the
project limits. A draft Stream Study and Wetlands Study have been completed and are attached
with this report. These studies describe the existing state of these streams and wetlands and outline
the role they play within the immediate area's ecosystem.
2.3.5 Subsurface Conditions
A preliminary subsurface investigation was conducted in the area immediately adjacent to the
tracks. The samples taken reveal Duwamish Floodplain Sand and Organic Deposits with underlying
strata of Deep Water Bay Deposits and Green River Alluvium. Existing groundwater elevations
were taken at two observation wells. The resulting elevations were significantly different; boring B-
1 indicted an elevation of 22, while B-3 showed an elevation of 15. This difference was likely due to
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South 180th Street Grade Separation 2 August 1999
the level at which the bore holes were sealed. Boring B-1 was sealed 20 feet from the existing
surface above an impermeable organic clay layer. The groundwater elevation of 22 is approximately
the same ground elevation of a wetland 40 feet east of the boring. This groundwater is likely a
perched aquifer above the clay layer. Boring B-3 was sealed 60 feet from the existing surface, below
the impermeable clay layer. The groundwater below the clay layer is likely an artesian aquifer. A
groundwater elevation of 22 will be assumed for this preliminary phase of the project. However,
additional observation wells and a detailed monitoring system should be instituted for the PS&E
phase.
Review of existing Federal Emergency Management Agency(FEMA)information and hydrological
reports indicate that this area of South 180th Street will be influenced by the 100-year event from
Springbrook Creek. It is important to note that all base plan information for this project is
referenced to the 1988 NAVD vertical datum. However,FEMA information and other reports are
based upon the 1929 NGVD vertical datum. The 1929 NGVD elevations are 3.53 feet lower than
1988 NAVD elevations. Using this adjustment, a conservative 100-year flood elevation of 21 has
been assumed based upon a FEMA flood elevation of 17.8. For a more detailed description of the
existing conditions,refer to the attached Draft Geotechnical Engineering Report.
2.3.6 Railroad
Currently,the existing railroad crossing consists of three sets of tracks owned by two different
companies. The BNSF operates two tracks and the UPRR operates one track. This corridor is a
major north-south route for both railroads resulting in approximately 60 crossings per day.
Both the BNSF and UPRR are also planning for significant expansion of their facilities along this
corridor. It is expected that two tracks will be added by BNSF in the near future. One of these will
be a commuter rail as part of an extensive network proposed by Sound Transit. The UPRR also
currently has plans to increase its presence in the area by adding another track.
3.0 ROADWAY IMPROVEMENTS
3.1 DESIGN PARAMETERS AND STANDARDS
All design was performed in accordance with the procedures and requirements set forth by WSDOT,
King County Department of Transportation, American Association of State Highway and
Transportation Officials (AASHTO), and the City of Tukwila. The requirements include not only
roadway standards, but also current guidelines for treatment of roadway drainage and
environmental mitigation.
The basis for all elements of the roadway is the proposed design speed. Based upon the functional
classification and the urban character of the area, a design speed of 40 mph was adopted for this
project. The design speed will control the establishment of both horizontal and vertical geometry.
3.2 TRAFFIC ANALYSIS
A comprehensive traffic report for the South 180th Street corridor was prepared by The TRANSPO
Group, Inc as part of this project and is attached. The report reviews the current conditions and
estimates future traffic volumes. Several analyses of the arterial and intersection levels of service
(LOS)were conducted for the four and six-lane options.
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South 180th Street Grade Separation 3 August 1999
The report shows minimal difference in the 2020 corridor LOS between the four lane and six-lane
configuration. Both the AM and PM peaks for six lanes operated at LOS D,while the four-lane
option had LOS D and E,respectively. These results are predicated on the presence of another east-
west connection between SR 181 and East Valley Highway in the area by 2020. The most likely
connection will be Strander Boulevard to the north. The City of Renton has identified the extension
of this roadway in their long range transportation planning. For this phase of the design, it is
assumed that this or another connector will be constructed by the year 2020.
The three intersections(SR 181, 72nd South, and Oaksdale)within the project limits were reviewed
as part of the report. The analysis of the 2020 volumes shows that the only difference in LOS
between the two alternatives will occur at the Oaksdale intersection. The six-lane configuration will
provide a higher LOS for both AM peak(C versus D)and PM peak(D versus F) as compared to the
four-lane roadway. The report suggests that at that time, a study investigation of the intersection
should be conducted. This could result in specific improvements(additional turning lanes;retiming
of the signal)that might improve the operation of the intersections.
3.3 ROADWAY SECTION
The proposed roadway will consist of four-through lanes,two in each direction,with a center left-
turn or median lane. This center lane will serve as a turning lane at the beginning and end of the
alignment. As the roadway passes under the tracks,the piers supporting the new bridges will be
located in this center lane and delineated as a median. See Figures 11 and 12 for typical cross
sections and roadway details.
Lane width is a key component of any roadway design. It is the governing factor in the driver's level
of comfort and traveling speed. Standard lanes vary from 10 to 12 feet,with slower roads having the
narrow widths and principal highways the wider lanes. After careful consideration to both the
traffic volumes and surrounding constraints, it was determined that 11-foot travel lanes would be
used for all through lanes. Shoulder width is also a big concern in the design of a roadway section.
Although the new road will not have a direct connection to the Interurban Trail, its proximity
indicates the possibility for a good amount of bicycle traffic. To accommodate bicyclists, the outside
lane in each direction will be 15 feet wide. The width of the center lane is based more upon the
bridge pier than traffic concerns. Initial indication is that the center piers will be columns sitting on
a pile cap, which is supported by a 4-foot-diameter secant pile wall. Protective barrier(guardrail or
jersey barrier) must also be provided on both sides of the column. It was determined that a 12-foot
center lane will be able to accommodate the pier. For consistency,this width was carried throughout
the length of the project.
3.4 ROADWAY ALIGNMENT
See Figures 13 to 16 for plans and profile of the proposed roadway improvements.
3.4.1 Horizontal
As described in Section 2.3.1, the existing roadway is five lanes at the limits of the project. This
allows for an easy match into the existing lane configurations. The proposed alignment consists of
two tangents with a slight angle point(less than 40 minutes). The angle point is necessary to match
the existing centerline at the project limits. The beginning of the project(western limit)is the
intersection at 72nd Avenue South, Station 50+10. The end of the project(eastern limit)is at
Station 66+70.
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South 180th Street Grade Separation 4 August 1999
3.4.2 Vertical
Unlike the simplicity of the horizontal alignment,the vertical design required an intricate
combination of design speed and clearance requirements. While maintaining minimum sight
distance requirements(K=60),the profile must also allow for at least 17.5 feet of vertical clearance
between the roadway and the railroad bridges. The result of these constraints is a long sag curve
centered approximately under the BNSF bridge. At Station 62+25±there is a large(21 by 12 feet)
elliptical metal pipe through which Springbrook Creek passes under South 180th Street. The profile
was designed so that no work would be required on this culvert.
The vertical profile was established based on a 5.5-foot bridge superstructure depth. Upon
development of the final design,it may be determined that this depth of structure could be less. In
correspondence with a shallower structure,the profile could be raised. See Section 4 for a detailed
discussion of the bridges.
3.5 BIKE LANES
The outside lanes of the proposed roadway will be 15 feet wide to more safely accommodate vehicle
and bicycle traffic. The corridor will be signed for bicycles,but the lane will not be striped for
bicycles.
3.6 PEDESTRIAN AMENITIES
Curb and gutter and sidewalk will be provided for pedestrians. The 6-foot concrete sidewalk will
extend for the length of the project on both sides. The proposed walk will tie into the existing
sidewalk at the project limits. This will create a continuous pedestrian facility from SR 181 to
Oaksdale Avenue.
3.7 INTERSECTIONS
Only minimal intersection work will be required for the project. Specifically,the southeast quadrant
of the 72nd Avenue South intersection will be reconfigured. The proposed design will require that
the existing traffic signal pole and mast arm be reset to the back of the proposed sidewalk. It also
appears that the existing traffic loops on the eastern and southern legs of the intersection will have
to be replaced due to the approach work in this area.
3.8 ACCESS AND DRIVEWAYS
Due to the significant change in grade along the corridor, extensive access reconstruction and/or
reconfiguration is required along the length of the corridor.
Direct access to South 180th Street for Building No. 7210 cannot be maintained. With a 7- to 10-foot
grade difference, even a driveway at the maximum slope (15 percent)would require taking the
building just to allow access to the property. However, access to this property can be provided off the
existing southern driveway to NC Machinery, Station 52+25±, left. The parking area behind the
building would also need to be reconfigured.
The access to the vacant Building No. 7220 can be provided several different ways. As shown on
Figure 12, the existing drive of No. 7210 can be reconstructed to allow for"through"traffic access to
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South 180th Street Grade Separation 5 August 1999
the adjacent property's parking lot. A second option is to construct a new driveway around the back
(north)side of Building No. 7220. The confined nature of either of these shared drivewaystparking
lots could limit the size of vehicles that could access Building No. 7220. If Building No. 7210 was
removed as part of this project,then more direct access can be provided to Building No. 7220. Like
the above options,the new drive would be off the existing southern driveway to NC Machinery.
However,without Building No. 7210 present,the new driveway would be located 90 feet closer
(south)to South 180th Street and would be a more direct connection to the building.
The large industrial facility at Station 53+50 on the south side currently has access to South 180th
Street via a drive at Station 54+30. As with the above properties,the large grade difference will not
allow for reconstruction of the driveway. The future lack of access to South 180th Street will not
have a significant impact on the property because there are multiple drives located off 72nd South.
On the eastern side of the tracks,there are two access points that will be reconstructed. The
northern driveway at Station 61+00 will require about 80 feet of total reconstruction based upon
current survey. This driveway is currently a construction entrance but will eventually be the
secondary access for a large industrial development under construction. The drive for the public
storage facility will be relocated east approximately 75 feet to create a four-way intersection with the
driveway described above. The property between the current drive and Springbrook Creek,onto
which the new driveway will be located,is currently classified as"open space." The relocation of this
driveway will require the purchase of a portion of this"open space"land.
In addition to the business and residence accesses, access will need to be provided to the area
between the tracks. The existing access from South 180th Street will be lost to the grade separation.
A private at-grade crossing will be needed over both the BNSF and UPRR. The crossing of the BNSF
will likely be an extension of the access road to the detention pond. The crossing of the UPRR could
be north or south of South 180th Street. This will be decided in Phase 2 when access to Building No.
7220 is finalized.
3.9 TRENHE SEAL
To obtain the necessary vertical clearance, the proposed underpass will require a significant length
of the proposed roadway to be below the normal groundwater elevation. To overcome the hydrostatic
uplift pressures associated with the groundwater, a gravity-based concrete seal must be constructed.
The concrete slab, called a tremie, will seal off the roadway from these subsurface conditions.
Comprised of lean, unreinforced concrete, the seal will be placed after the secant pile walls and
excavations are completed and before dewatering. Using tremie concrete, an extensive groundwater
pumping system will not be required.
The location of the tremie seal below the roadway profile was based upon the cover required for
proposed utilities. It was determined that a thickness of 6 feet below the proposed grade and above
the tremie will allow for construction of the drainage, water, and gas systems. The tremie seal is
designed for a factor of safety of 1.1, based upon the recommendations of the Draft Geotechnical
Engineering Report. As stated in Section 2.3.5, an elevation of 22 was assumed at this stage of the
design. Due to the importance of this elevation, more detailed hydraulic and hydrological study is
recommended prior to the final design to better ensure the accuracy of the groundwater elevation. A
series of well points strategically placed within the underpass limits should be installed to monitor
the groundwater elevations and fluctuations.
To ensure that the seal will not float during placement, the tremie design must take into account the
presence of the groundwater level during construction. That is, the tremie seal must have enough
buoyancy resistance(weight)to counteract the hydrostatic force of the groundwater. To totally
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South 180th Street Grade Separation 6 August 1999
contain the underpass, a"backwall"will be constructed at the east and west limits of the seal. The
top elevation of this backwall will be set at 22 feet. In conjunction with the weight of the tremie seal
itself,the 5-foot-thick layer of gravel can be placed before the water is pumped out and therefore,
used as counterweight to the hydrostatic force of the groundwater. Preliminary investigation
indicates that uplift resistance due to friction between the tremie seal and the wall,and that
provided by center piers will also contribute to the force resisting the hydrostatic pressure. However,
until a detailed investigation is conducted in the final design,this additional resistance has been
disregarded in the preliminary design.
Disregarding the safety factor,this design implies that the seal will float if the groundwater rises
above 22 feet. To ensure this will not happen,an underdrain system will be installed outside of the
walls at an elevation of 22 feet. This system will discharge into Springbrook Creek and will work as
long as Springbrook Creek is below 22 feet. Because the 100-year flood elevation of the creek is 21
feet,the system should work fine. However,in the event Springbrook Creek's level does exceed 22
feet,the underpass will be allowed to flood in order to prevent the major damage which would result
from the seal floating. The creek bank just east of the Public Storage driveway will be graded to an
overflow elevation of 22 feet. If the creek level does rise to 22 feet(one foot above the top of the
South 180th culvert),it will overflow the bank into the underpass. The weight of the water inside
the underpass will counter the excess buoyant force on the seal. If this does occur,the City will have
to close the road,turn the pumps off, and be sure the overflow is not sandbagged or raised in any
other way. -71
3.10 DRAINAGE
Roadway drainage is one of the most important design elements of this project. The following is a
summary of the drainage analysis as described in the attached Draft Technical Information Report.
A system of catch basins and closed lines are proposed to collect and convey runoff. The runoff
collected from the depressed roadway will be pumped to a new stormwater facility for water quantity
and quality treatment. See Figure 17 for the preliminary design of this facility. The proposed
system was analyzed and designed in accordance with the current guidelines listed in the King
County Surface Water Design Manual (KCSWDM). The project will add approximately 0.5 acre of
new impervious surface to the site. Rational Method was used to compute peak discharges for all
pipelines and to determine pump station requirements. The system was designed to accommodate
the 25-vear storm, 4.6 cubic feet per second (cfs). Gutter flows and inlet spacing were determined by
using the method listed in the Washington State Department of Transportation(WSDOT)
Hvdraulics Manual. Backwater Analysis method was used to analyze the new system to verify
adequate capacity. Below is a brief description of the proposed drainage system.
3.10.1 72nd Avenue South (Station 51+00) to Station 52+08
No modifications are proposed to the existing system west of 72nd Avenue South. The existing
roadway storm sewer system east of the intersection must be removed due to the proposed grade
difference. New catch basins and 12-inch pipe will collect and convey runoff from Station 52+08 to
the west. This system will be tied into the existing system on 72nd Avenue South.
3.10.2 Station 52+08 to Springbrook Creek Culvert (Station 62+80)
Runoff will be collected by catch basins along the gutter on both sides of the roadway. The mainline
of 12-inch pipe will convey the flow to the underground pump station located approximately at
Station 58+25, under the north sidewalk. The lift station will be an alternating duplex pump
system. That is,the chamber will have two pumps that alternate pumping the runoff. This allows
for not only even wear on both the pumps,it also provides for a backup pump during the
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South 180th Street Grade Separation 7 August 1999
maintenance or replacement of one pump. In conjunction with the pump redundancy,the final
design phase will investigate the feasibility of providing a second source of power to operate the
pumps. The runoff will be pumped to the new stormwater facility located approximately 50 feet
north of South 180th Street and east of the tracks for water quality and water quantity control.
Discharges from the new facility will be conveyed via a proposed outlet structure and drainage pipes
under the existing driveway at Station 61+00 to Springbrook Creek.
3.10.3 Springbrook Creek Culvert (Station 62+80) to End of Project (Station 66+70)
No major modifications are proposed to the existing system within this section. New catch basins
will be connected to the existing system on both sides of South 180th Street.
3.10.4 Groundwater Seepage Within Limits of Underpass
While the tremie seal and secant pile wall are designed to prevent the presence of groundwater
within the roadway prism,it is likely that a small amount will infiltrate the joints in the wall and
the tremie seal. To collect this water, a combination of drain rock and 6-inch perforated pipes will be
used, see Figure 12.
3.10.5 Combined Detention and Wetpond
To meet the water quality requirements,the collected stormwater will be discharged into a
combination detention and wetpond. The lower elevation of the pond will provide water quality for
the runoff while the upper level provides the detention capacity required. The new pond was
designed assuming 3H:1V interior slopes, 2H:1V exterior slope with 1 foot of freeboard. An
emergency overflow was provided to discharge the 100-year flow for developed condition. Access will
be provided for any future maintenance.
3.11 UTILITIES
There are several utilities that must be relocated in conjunction with the proposed grade separation
project. As described in Section 2.3.2, most of the utilities are primary feeds for the area and must
stay operational for the duration of construction. It is imperative that the utility owners, the
contractor, and the engineer closely coordinate during final design and construction. The sequencing
of these replacements is an important aspect of the overall construction. See Section 7 for a detailed
discussion of the construction phasing.
3.11.1 Sanitary Sewer
The existing sanitary sewer system west of the tracks must be relocated due to the grade revision to
South 180th Street. A new 8-inch main will be run north along the NC Machinery driveway at
Station 52+35±, left. From there, the system will turn east behind Building No. 7220 and tie into an
existing sanitary manhole.
The existing eastern system begins at the recently constructed Public Storage facility. The large
roadway cut adjacent to the property and the presence of the Springbrook Creek culvert will not
allow for the construction of a replacement gravity system. Therefore, a small pump station will be
required to provide service for this facility.
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South 180th Street Grade Separation 8 August 1999
3.11.2 Water Lines
There are two scenarios for the construction of a proposed water main. The first option is to
construct a bypass on the northern side of the project. This temporary line will pass under the
railroad tracks north of the project location. Any relocation of the waterline under the railroad
tracks will require a steel pipe sleeve. To minimize disruption,it is likely that the sleeve will be
jacked. After completion of the bridges, a 12-inch main will be constructed within the new roadway,
eliminating the bypass. This alternative is shown in the figures in Volume 2 of this report.
The second alternative would be to maintain the temporary bypass described above as the ultimate
location of the water main. This will eliminate the need to"relocate"the line into the roadway
section,thereby reducing the construction cost to the owner. There are drawbacks to this option.
Any utility crossing of the railroad property outside the roadway ROW will require an easement
between the utility owner and both BNSF and UPRR. The issue of access is also a big consideration.
Any future maintenance that would require work within the railroad property would be very costly.
If a full-fledged repair is warranted,it is likely that a new crossing would be required by the
railroads rather than allowing the utility owner to disrupt train traffic. This option must be
thoroughly reviewed by both the owners and the railroad before a decision is reached.
3.11.3 Overhead Power Lines
The preferred grade separation will not require any revisions to this existing aerial utility.
3.11.4 Buried Power Lines
The existing buried power lines along this corridor supply electricity to properties adjacent to South
180th Street and the roadway lighting system. Before service is disconnected for the duration of the
project, temporary services must be provided for the properties. The simplest and least expensive
option would be temporary poles and aerial connections. No provisions will need to be made for the
roadway lighting, as the road will be closed during construction. Upon completion of the bridges,
new underground power lines will be constructed to reestablish service to the properties and supply
power for new roadway lighting.
3.11.5 Gas Line
As with the water main,the existing gas line is a primary feed and must remain operational.
Similarl}I, there are two alternatives for relocation that must be further explored. This will require
construction of a temporary bypass. The first option is to construct a gas main bypass. Figures 13 to
15 show this main south of the project. However, it is possible that the temporary water and gas
could -share" a trench and the sleeve crossing under the railroad tracks. This would be basically half
the trenching and jacking needed for the construction of these temporary feeds. A new 16-inch
pipeline will be constructed within the roadway upon completion of the bridges. Just like the water
main, the second alternative would maintain the temporary bypass described above as the ultimate
location of the gas line.
3.11.6 Buried Telecommunication Lines
The fiber optic lines between the tracks will need to be relocated prior to the start of construction of
the underpass. Three primary locations have been considered for the relocations. First is for each
individual owner to bore their cable under the lowest elevation of the secant pile wall. Second is for
one or more of the companies to lease space in a duct bank being built in late 1999 under the walls.
Third is to build the pedestrian bridge first and then relocate the fiber optics under that bridge. This
is the option shown in the figures.
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South 180th Street Grade Separation 9 August 1999
Local phone service will need to be relocated prior to construction. If needed,it can then be
permanently relocated when the project is complete.
3.11.7 Olympic Pipeline
Relocation of the Olympic Pipeline will be required due to the retaining and abutment wall
construction where the line crosses South 180th Street. As with the fiber optic lines,the fuel line
will either be relocated to the Interurban Trail bridge or below the walls during the preliminary
phases of the project.
3.12 RETAINING WALLS
Due to the significant grade differential between the preferred alternative and the existing roadway,
retaining walls will be needed along both sides of the road for nearly the entire length of the project.
These retaining walls will not only serve the conventional use of retaining soil,but will also be used
as the abutments(foundations)for the railroad and trail bridges that pass over the roadway.
Several types and methods of construction for the wall system were investigated. It was determined
that the most economical method was the use of secant piles for the large excavation areas. This
section discusses retaining walls that resist lateral pressures and loads only. See Section 4 and the
Geotechnical Engineering Report for a detailed description of the secant pile walls acting as the
bridge substructure system.
Secant pile walls consist of a row of 4-foot-diameter drilled shafts, alternating between the primary
and secondary pile, working in conjunction as a single wall. Figure 20 shows a sketch of the
preliminary wall configuration. The primary piles are placed 6 feet apart on center and cast with
lean, unreinforced concrete. The secondary piles,with conventional steel reinforcing bars, steel
wide-flange, or HP sections, is drilled midway between the primary piles, overlapping the edges by
about 1 foot.
The shaft penetration depths (bottom elevation of the shaft)were determined based on lateral
pressures recommended in the Draft Geotechnical Engineering Report, Section 6.3.1. The subsurface
explorations were conducted in a limited area near the proposed bridge structures. The results were
then extrapolated for the entire project limit. To avoid encountering unexpected soil, it is
recommended that additional subsurface information of the site be obtained for the final design
phase of the project.
To assist in resisting the significantly high lateral loads, permanent reinforced concrete struts will
be constructed. These struts will "connect" to the secant pile walls at the wall cap and will span
across the entire roadway. The limits (east and west)of the struts is governed by the need to
maintain minimum vertical clearance. A height of 16 feet 6 inches is required along the roadway.
Based upon the preliminary roadway profile, struts can be constructed from Station 55+20 to Station
58+80. Within the limits of the struts, approximately 30 percent of the wall height(or shaft) are
required to be under the bottom of the tremie elevation. For walls without lateral struts, about half
of the shaft height needs to be below the bottom of the tremie seal. The use of struts will greatly
reduce the wall heights required. During the final design, a detailed investigation of the strut
locations will be undertaken to ensure maximum utilization. If permitted by the railroads,the
bridges may be used as struts.
In the initial stages of the design, it was assumed that a more conventional retaining wall system
would be used at the limits of the roadway cut. Specifically,this is the area where the exposed wall
heights are less than 7 feet. It was thought that this would result in smaller,less expensive walls.
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South 180th Street Grade Separation 10 August 1999
However,replacing secant pile wall with conventional retaining walls was disregarded for the
following reasons.
■ Regardless of the exposed wall height, the footing would have to be at an elevation below the
bottom of the tremie seal.
■ The limits of excavation for placement of the wall footings would be greater than compared with
secant pile wall construction. Existing adjacent properties may be further impacted than that
already required by secant pile wall.
3.13 SECANT PILE AND PIER FACADE
The secant pile wall and pier facades will be precast concrete vertical panels. These units will be
approximately 10 feet wide and have an architectural finish. The panels will be supported vertically
on the tremie seal,which will act as the footing. This requires the wall fascia be extended
approximately 6 feet below the finished roadway grade to the top of the tremie seal,thereby,
eliminating the need to construct any additional footings in the subgrade layer. In order to provide
lateral and buckling stability,the facade will be supported by connections to the adjacent secant pile
walls. This support is critical, especially near the bridge locations where the wall height reaches
approximately 30 feet. Closely spaced weep holes along the fascia walls near the top of the tremie
seal will allow for the drainage of the gap between the wall and the facade. An underdrain on each
side of the roadway will collect any water from these weep holes. Vertical gaps(construction joints)
at set intervals are necessary to allow for possible isolated settlement of the wall. Also,the
connection between the fascia and secant walls must be designed to allow independent settlement of
the two walls. The top of the facade will be below the soffit of abutments in the bridge areas and
below the wall cap for the remaining areas. It is assumed that the wall facade will be vertical with
no slope. This avoids pushing the walls away from each side of the roadway and, thus,reduces
construction cost.
3.14 RIGHT-OF-WAY/EASEMENTS
This project will require that permanent land takings and temporary construction easements be
obtained. The existing ROW is very inconsistent,varying from approximately 60 to 100 feet in
width. Figures 13 to 16 show the existing and proposed ROW for the corridor.
Due to the construction of the secant pile walls, an existing house will be taken as part of this
project. The existing house on the south side of the roadway,west of the Interurban Trail,would be
within 2 feet of the wall and would lose access to South 180th Street. As a result, the house cannot
remain with the proposed construction.
All other permanent takings associated with the project are land takings. Upon completion, the City
must "own" all sidewalk areas and corresponding retaining walls for liability and maintenance
reasons. This includes the sidewalk required to access the Interurban Trail.
To access the construction areas, temporary easements will be needed along the entire corridor.
These are short-term easements that will last for the duration of the project. The main purpose is to
allow construction equipment to access the work site.
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South 180th Street Grade Separation 11 August 1999
3.15 SPRINGBROOK CREEK CULVERT REPLACEMENT
Prior to 1980, South 180th Street crossed Springbrook Creek on a concrete bridge. In 1980, the
roadway was widened and the bridge was replaced with a 21-foot-wide by 12-foot-high by 150-foot-
long arch culvert. In addition to the arch culvert, a four-cell 50-foot-wide by 12-foot-high by 60-foot-
long concrete box culvert was constructed 150 feet to the east. The cities of Kent and Renton jointly
funded this culvert. Its purpose was to handle a proposed realignment of Springbrook Creek and to
handle increased creek flows associated with future development within the Springbrook Creek
basin. The box culvert has been buried under the roadway since 1980.
Due to development and environmental restrictions,the proposed realignment of the creek to the
west is no longer possible. The box culvert also interferes with proposed construction of the
underpass and will require removal during construction of the underpass. Although the realignment
function of the box culvert is no longer needed,the increased capacity function will be needed in the
future. The cities of Kent and Renton have performed basin studies for Springbrook Creek. Both
studies indicate future development, 100-year flood flows that will result in a creek level upstream of
the culvert of Elevation 23.1 feet. Any creek level over Elevation 22 feet will flood the underpass and
should therefore be avoided if possible.
A study will be performed early in Phase 2 to determine the best way to provide increased hydraulic
capacity for Springbrook Creek under South 180th Street. Three alternatives will be studied: a
bridge to replace the arch culvert in its present location,realigning the creek through a new culvert
just east of the arch culvert, and maintaining the existing arch culvert while adding a smaller
culvert just to the east to handle high flows. These alternatives are not shown in the figures in
Volume 2 because of the uncertainty of the final solution.
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South 180th Street Grade Separation 12 August 1999
4.0 BRIDGES
4.1 INTRODUCTION
Bridges proposed for this project include a pedestrian bridge,two railroad bridges and, if pursued, a
shared access road bridge for railroad maintenance equipment. A baseline alternative was defined
in order to meet the budget for this project. The permanent bridge components of the baseline
alternative includes bridges for existing track and trail conditions.
■ An Interurban Trail pedestrian bridge
■ A one-track UPRR bridge
■ A two-track BNSF bridge
A temporary bridge is required as part of the temporary shoofly for the BNSF tracks.
Alternatives that include wider railroad bridges that accommodate more tracks and the addition of
an access road bridge that would be shared by the BNSF and UPRR were evaluated for feasibility
and construction costs. These alternatives are presented as additive alternatives.
■ Alternative Al—Adding the foundation and substructure only for a second UPRR track.
■ Alternative A2—Adding the foundation, substructure and superstructure for a second UPRR
track, i.e., constructing a two-track bridge.
■ Alternative B1—Adding the foundation and substructure for a third BNSF track to the east of
the existing BNSF tracks for future Sound Transit use.
■ Alternative B2—Adding the foundation, substructure and superstructure for the third BNSF
track, i.e., constructing a three-track bridge for future Sound Transit use.
■ Alternative B3—Adding the foundation and substructure for a fourth BNSF track to the west
of a three-track BNSF bridge.
■ Alternative B4—Adding the foundation, substructure and superstructure for the fourth BNSF
track, i.e., constructing a four-track bridge.
■ Alternative Cl —Adding the foundation and substructure for an access road bridge.
■ Alternative C2—Adding the foundation, substructure and superstructure for the access road
bridge.
In these alternatives, substructure consists of all structures below the girder bearings. For a two-
span bridge, the interior pier substructure includes the secant pile wall and pile cap foundations,
columns, and cap.
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South 180th Street Grade Separation 13 August 1999
4.2 INTERURBAN TRAIL BRIDGE
4.2.1 Pedestrian Bridge Design Parameters and Standards
The design of the Interurban Trail Bridge conforms to current AASHTO parameters and standards.
Listed below is a summary of the design parameters.
Type: Various options, see below.
Width: 10 to 12 feet
Span length: 81't single span
Purpose: Pedestrian and bike trail
Restriction: No motor vehicles
Superimposed Dead Loads: 14" diameter fuel line,4-4" PVC fiber optic lines, and railing
Live Load: 85 psf
4.2.2 Location of Bridge
The proposed Interurban Trail bridge will be constructed along the current alignment of the path
and is centered at Station 55+40.
4.2.3 Description of Bridge Alternatives
In investigating the bridge alternatives for the Interurban Trail,three different types of single span
bridge were considered. These options include a 10-foot-wide precast concrete double tee section, a
12-foot-wide steel I-beam section, and a 12-foot-wide prefabricated truss bridge. Below is a detailed
description of the alternatives.
Precast Double Tee
A standard 10-foot-wide, 38-inch-deep, 6-inch-thick slab double tee section was investigated due to
its convenient availability in this region. Also,the section configuration will allow the utilities to be
conveniently"hidden" between the tees. Concrete structures,in general, require the least
maintenance throughout the bridge design life. At 10 feet wide, the bridge will be narrower than the
existing trail. A transition from 12 to 10 feet will have to be provided at both approaches. It will
also be necessary to post signs to warn bikers.
Steel I-Beam
A typical I-beam section steel bridge layout was considered. The configuration consisted of 3-
W33x118 beams at 4-foot spacing with 6-inch steel form concrete deck. The 12-foot-wide bridge
would have channel cross-frames spaced every 10 feet that could be used to support the utilities.
The exposed steel must either be painted or weathering steel must be used.
Prefabricated Steel Truss
There are several manufacturers that produce prefabricated steel truss bridges of various
configurations. The biggest advantage of this option is its easy installation. The bridge will be
delivered to the site completely assembled, therefore, minimal equipment and labor hours are
required. Cost is very compatible with the concrete option. The truss can come factory-primed and
painted or be made of weathering steel that requires minimal maintenance.
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South 180th Street Grade Separation 14 August 1999
4.2.4 Substructure/Foundations
The Interurban Trail bridge was designed to span across the full proposed roadway width. The
structure will be supported by abutments seated on top of the walls on each side of the proposed
roadway. Preliminary design for the foundation wall penetration was based on recommended lateral
pressure and axial load capacity for the pier as shown in the Draft Geotechnical Engineering Report,
shown in Figures 7,8,9, and 11. The foundation walls will be drilled shafts of 4 feet in diameter.
4.2.5 Evaluation of Bridge Alternatives
The selection of the bridge type for the Interurban Trail was based upon four criteria: cost, ease of
construction,maintenance, and aesthetics. Listed below is a summary of the findings.
Precast Double Tee
Cost Using"in stock"standard precast sections results in this alternative being the
least expensive.
Construction The double tee can be delivered to the site in one piece. Installation of the railing
system and wearing surface of the deck will occur in the field. The use of
temporary shoring will not be required.
Maintenance Concrete structures, in general,have low maintenance requirements throughout
bridge design life.
Aesthetics The concrete structure will be consistent with the railroad bridges and presents a
clean look with utilities conveniently"hidden"between the tees.
Steel I-Beam
Cost This option will be the most costly due to the multiple components (beams, cross
frames, deck, etc.)of the bridge.
Construction The bridge superstructure will likely be field spliced. Installation of the railing
system and wearing surface of the deck will occur in the field. The use of
temporary shoring will be required if the beams are field spliced.
Maintenance The maintenance costs associated with this option will vary depending upon the
type of steel selected. Painted steel will have significantly higher associated costs
as compared to weathering steel.
Aesthetics This option will provide a look very similar to standard steel roadway bridges.
Prefabricated Steel Truss
Cost This alternative is slightly more expensive than the precast concrete option.
Construction The steel truss will be delivered to the site in two sections. Assembly of the
sections is very simple. The unit will come with the railing system already
installed. A concrete deck would be poured in the field. Erection of the unit will
be minimal.
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South 180th Street Grade Separation 15 August 1999
Maintenance The maintenance costs associated with this option are very inexpensive. The use
of weathering steel will greatly reduce the costs as compared to the other
alternatives.
Aesthetics In conjunction with the low construction cost and ease of erection,the main
feature of a prefabricated truss is its aesthetics. This type of bridge will present
a very distinctive look. Figures 18 and 19 show the plan and elevation view of
the bridge.
Based upon the above evaluation,it is suggested that a prefabricated steel truss be used for the
superstructure of the Interurban Trail bridge. Several manufactures produce a wide variety of
bridges.
4.3 RAILROAD AND ACCESS ROAD BRIDGES
4.3.1 Design Parameters and Standards
The design of the railroad bridges conforms to the following manuals and design guidelines.
■ American Railway Engineering Association(AREA)Manual for Railway Engineering,
(Manual)1997 edition
■ Guidelines for Design and Construction of Grade Separation Underpass Structures, UPRR,
March 31, 1998
■ Standard Plans, BNSF, November, 1998
■ Standard Plans,UPRR
■ Bridge Design Manual, WSDOT
■ AASHTO Standard Specifications for Highway Bridges, 16th edition and 1997 and 1998 Interims
Geometric requirements for the railroad bridges are as follows.
■ Vertical clearance above roadway: 16 feet 6 inches with sacrificial beam, 17-foot 6-inch
minimum without sacrificial beam. In both instances a collision impact device will be attached
to the exterior beams of each bridge.
■ Horizontal spacing of adjacent tracks: 15-foot minimum between track centerlines.
■ No obstructions are allowed between tracks such that the tracks can be relocated to any
alignment on the bridge.
■ Minimum horizontal clearance, center of tracks to railing posts, 10-foot 2-inch minimum.
■ Grades and elevations based on 1 inch for waterproofing, 8-inch ballast under the tie and a 7-
inch deep timber tie. Elevations for the structures to be carried from top of tie.
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South 180th Street Grade Separation 16 August 1999
Railroad bridge dead loads requirements are as follows.
■ The permanent railroad bridges shall be designed with ballasted decks.
■ Ballast at the UPRR bridge: 15 inches deep initially,and designed for a future condition of 30
inches maximum(120 pcf).
■ Ballast at BNSF bridge: 15 inches deep initially,and designed for a future condition of 24-inch-
thick maximum(120 pcf).
■ Railroad standards require that no utilities will be supported by the railroad structures.
Railroad bridge live and impact loads: Cooper E 80 loading with diesel impact per the AREA
Manual.
■ Prestressed concrete to be designed in accordance with Chapter 8,Part 17.
■ Impact calculated for prestressed concrete spans to be used as applicable for design of
substructure units.
■ Steel spans shall be designed for Cooper E 80 or the Alternate Live Load,whichever governs.
Substructure for steel spans to be designed for Cooper E 80 loading.
■ Impact calculated for steel spans to be used as applicable for design of substructure units.
Criteria for the temporary railroad bridge(BNSF crossing of Mill Creek, south of South 180th Street)
are as follows.
■ Structure can be either treated timber, untreated timber or steel.
■ Open-deck construction can be used.
■ Design for Cooper E 80 loading in accordance with the appropriate AREA Manual chapter for the
type of material used.
■ The temporary bridge is to be removed and the permanent structure left in the original initial
condition upon completion of project construction.
Waterproofing of the railroad bridge superstructures will conform to the AREA Manual, as well as
UPRR and BNSF requirements. This system includes a waterproof membrane protected by two
lavers of asphalt impregnated planks staggered and laid at 90 degrees to each other. The membrane
is held to the top of girder with compatible mastic. Each layer of asphalt planks are set in mastic
compatible with the membrane as well as the planking.
The access road bridge design will conform to current AASHTO and WSDOT requirements. Design is
for a single HS20-44 truck on a 12-foot-wide lane. No utilities are to be supported by the access road
bridge. A 2-inch asphalt overlay of the concrete girder top surface is assumed.
Seismic loading for railroad and access road bridges: site peak ground acceleration(PGA) =0.32 per
the Shannon & Wilson Draft Geotechnical Engineering Report representing a 10 percent chance of
exceedance in 50 years(return period of 475 years). Soil type AASHTO Type IV with a
corresponding site factor of 2.0. Design will be in accordance with AREA Manual, Chapter 9 and
AASHTO Standard Specifications.
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South 180th Street Grade Separation 17 August 1999
A minimum of three shoofly tracks at 15-foot centers is required for temporary train detours during
construction. Minimum clearance from centerline track to shoring is 10 feet.
Work performed on railroad right-of-way xequires all workers to be trained in accordance with the
FRA Roadway Worker Protection rules. Work outside 25 feet from the centerline of an active track
does not require a railroad flagperson to be present. Work being performed within 25 feet from the
centerline of an active track requires a railroad flagperson to be present.
4.3.2 Location and Description of Bridge Alternatives
Figure 21 shows the layout of the proposed railroad bridges for the baseline alternative. The
proposed bridge structures are oriented at approximately 90 degrees to the South 180th Street
alignment. Both the UPRR and BNSF tracks intersect the South 180th Street alignment at a slight
skew angle as shown in the Figures. The UPRR one-track bridge will be constructed at the current
alignment of the existing UPRR Track,with the bridge centered at the track intersection with the
South 180th Street alignment at Station 56+20.84. The overall width of the UPRR concrete
superstructure for the single track option is 19 feet. The location of the BNSF two-track bridge is
based on the existing alignment of the westerly BNSF track, designated BNSF Track 1. The existing
east track,Track 2,will be realigned parallel to the Track 1 alignment,with 15-foot track centers.
The BNSF bridge is centered between these two tracks and has an overall width of 36 feet 8 inches.
Figure 22 illustrates the full buildout alternative,which includes a two-track bridge for the UPRR, a
4-track bridge for the BNSF, and a shared access road bridge between the two railroad bridges. The
layout and orientation of the railroad bridges are similar to that of the baseline alternative.
Noteworthy features include:
■ In Figure 22, the future UPRR Track 2 alignment is shown east of and parallel to the existing
Track 1 alignment. Discussion occurred during this project phase concerning locating the future
UPRR track west of the existing track instead of east. Locating the future track to the west
keeps the UP tracks within the existing UPRR ROW. A westerly alignment may provide a
simpler track design and alignment. However,the west alignment does move tracks closer to the
high voltage power lines and the Interurban Trail.
■ The future BNSF tracks are"outside" of and parallel to the existing two BNSF tracks. Based on
preliminary design plans for the Sound Transit commuter rail line received from BNSF(plans
dated 11/2/98), the easternmost Track 3 will serve as the Sound Transit commuter rail line.
Future Track 4, to the west of Track 1, would serve BNSF. All tracks are offset from the existing
Track 1 alignment in increments of 15 feet
■ The access road bridge is shown located at mid-distance between the future UPRR Track 2 and
the future BNSF Track 4. The location of the access road bridge can be adjusted to the east or
west.
Figure 23 is an elevation of the railroad or access road bridges. Total out-to-out length of the bridge
structures is expected to be 88 feet 4 inches. The overall structure length is based on the following.
■ The roadway section along South 180th Street.
■ Construction of 4-foot-diameter secant pile wall support for bridge abutments and piers.
■ A 14-inch allowance for the fascia wall in front of the secant piles and its connection to the piles.
■ An allowance for the abutment pile cap extending 6 inches beyond the secant piles.
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South 180th Street Grade Separation 18 August 1999
4.3.3 Superstructure Types and Evaluation
Superstructure types for the railroad bridges were identified and evaluated in a two-step process.
Initially, superstructure types for a single span railroad bridge approximately 86 feet long and for a
two-span bridge with spans of approximately 43 feet were evaluated at a conceptual level. Criteria
used to evaluate these types included cost,constructability,flexibility for future bridge widening,
effects on foundation types, and superstructure depth as it affects excavation. Next,the two-span
superstructure types were studied further to determine a preferred type. Through this evaluation, a
two-span,prestressed,precast concrete girder alternative was recommended to and approved by the
TAC.
Typical superstructure types for single span and two-span bridges are as follows.
Single-Span Superstructure
■ Steel deck plate girder(DPG)with or without a composite concrete deck.
■ Steel through plate girder(TPG)with or without a composite concrete deck or with a steel
ballast pan deck.
■ Precast,prestressed concrete single cell box girders,post-tensioned transversely to ensure that
the individual box girders act as a unit, i.e., share live load equally.
Two-Span Superstructure
■ Steel TPG with or without a composite concrete deck or with a steel ballast pan deck.
• Steel wide flange beam span with or without a composite concrete deck or with a steel ballast
pan deck.
■ Precast, prestressed concrete double-cell box girders.
■ Precast, prestressed concrete single-cell box girders.
A comparison of the single-span and two-span alternatives resulted in the following findings.
■ A single span superstructure results in high vertical loads at the abutments. If only the Baseline
Alternative is constructed, the secant pile wall scheme may be used to support the bridges.
However, if the full buildout alternative is constructed, the deeper drilled shaft foundation
alternative may be required to support the larger vertical loads.
■ In general, the depth of the superstructure girder is approximately 1 inch of depth per foot of
span length for both concrete and steel options. Hence, the 86-foot-long single span is deeper
than two 43-foot spans. For longer spans, the net depth of a steel TPG bridge measured from top
of tie to bottom of the girder is less than or equal to the depth of a concrete girder bridge. The
net depth of an 86-foot single-span steel TPG is about the same as the depth of a 43-foot
prestressed concrete girder. Because reducing the superstructure depth is the key to reducing
the depth of excavation for the roadway,the steel TPG appears attractive due to its relatively
shallow net depth.
■ A typical steel TPG cross-section for carrying multiple tracks includes a through girder between
the tracks. This interior girder creates an obstruction between the tracks,which makes
realigning the tracks or placing crossing tracks impossible. In widening for future tracks,the
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South 180th Street Grade Separation 19 August 1999
exterior through girder becomes an interior through girder,creating a similar obstruction. Also,
during construction of a widening,any existing tracks on the bridge that are adjacent to the
widening will be out of service because the floor system connections to the steel girder will
require removal and reassembly. These disadvantages of the through girder section negates its
apparent advantage of shallower net depth.
■ If the girder spans serve as permanent struts across the excavation,the center pier of the two
span alternative provides a brace for the struts,thereby reducing the unbraced length of the
compression struts.
■ The center pier for the two-span alternative can be located in the median(center)lane of the
South 180th Street roadway section. Reinforced concrete traffic barriers to shield the piers from
vehicles can also be accommodated in the median lane.
Based on these findings, a two-span structure was preferred. Superstructure types for this option
were compared further using"standard of the industry"costs per track foot,constructability and
flexibility in widening for future tracks. Dollar values used are conceptual level construction costs
which include construction of superstructure and substructure for typical railroad bridges.
Evaluation resulted in the following conclusions.
■ The steel TPG option,while capable of matching span depths with the other options,would
create obstructions between tracks. Typical unit construction costs are approximately$6,000 per
track foot.
■ A steel wide flange beam span provides the flexibility of no obstructions between tracks on a
bridge. Train traffic could be slightly affected when future expansion of a bridge occurs. Unit
construction costs typically range around $4,500 per track foot.
■ Precast, prestressed concrete double-cell box girders provide a less expensive option than the use
of steel spans. However, these girders are typically 7 feet wide with a stem depth of at least 42
inches. Typical double-cell box girder construction costs about $3,000 per track foot.
• Precast, prestressed concrete single cell box girders used by the BNSF are 3 feet 2 inches wide.
Their smaller width offers more flexibility in bridge widening for additional tracks. They weigh
approximately half of the double-cell box girder weight and, therefore, are easier to handle in the
field. Depending on the detailed design criteria used, the depth of the spans would be either 36
or 42 inches, respectively. Typical construction costs range around $3,000 per track foot. The
single-cell girders provide a more efficient match with structure geometry.
As a result of this evaluation, precast prestressed concrete single-cell box girders are recommended
as the superstructure type for the railroad and access road bridges. Although similar in cost to
double-cell box girders, the single-cell box girders are more efficient in matching the proposed track
geometry for this project. They also better satisfy the desire to have the option of widening the
bridges in the future. Local and regional precast concrete fabricators can provide this girder. Costs
for these girders obtained from local suppliers were used to develop construction cost estimates.
We note in this report that BNSF and UPRR use different detail design criteria for the box girders as
beams. BNSF designs single cell spans using the following parameters.
• A combination of two adjacent girders is designed to carry a Cooper E 55 loading.
■ All four girders supporting a track are designed to carry a Cooper E 80 loading.
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South 180th Street Grade Separation 20 August 1999
■ BNSF depends entirely on the transverse post-tensioning rods to create the shear friction
between girders to create composite action.
■ A maximum depth of 24 inches of ballast is used.
The UPRR detail design criteria requires the following.
■ The Cooper loading is spread over the length of railroad tie plus the depth of ballast below the
tie. This means that approximately three girders are used to carry the Cooper E 80 loading.
■ A shear key and epoxy grout is used between girders in addition to the transverse post-
tensioning rods to create composite action.
■ A maximum of 30 inches of ballast is used.
The differences in detailed design will be finalized during the PS&E phase after further meetings to
explain and obtain final railroad agreement for the substructure approach and discuss
superstructure issues. It is recognized that greater project economy could be realized by
constructing the bridges using the same components. The girder depth resulting from each
railroad's approach can be accommodated at the level of development of project geometry at this
project phase.
Substructure/Foundation Issues
Three foundation types for the railroad bridges were evaluated.
■ Drilled shafts
■ Diaphragm walls constructed using the slurry method
■ Secant pile walls
Drilled shafts were the most expensive alternative based on the deeper depth and size of the shafts
required to support the vertical (gravity) loads. The shafts would need to extend to a deeper
alluvium layer that is about 115 feet below the existing ground level. This shaft length is at the
upper end of typical shaft construction. Diaphragm or secant pile walls can extend into an upper
alluvium laver that ranges from 40 to 60 feet thick and is located approximately 50 feet below
existing ground. The relatively long length of the diaphragm or secant pile wall will distribute
gravity loads to the upper alluvium layer. The diaphragm walls using the slurry method were found
to be more expensive than the secant pile walls, in part due to lack of contractors available in the
Northwest familiar with this type of construction. Hence, secant pile walls were studied in more
detail and they were used to estimate construction costs.
Abutments consist of secant pile walls with a pile cap (Figure 23). The bridge girders are supported
on elastomeric pads set on the pile cap. The secant pile walls serve as lateral support for the
excavation during construction and in the permanent condition. In addition to distributing vertical
loads to the secant piles, the pile cap also acts as a wale,transferring lateral earth pressures to
horizontal compression struts needed to brace the excavation. It is possible that the bridge girders
can be used as struts during construction and in the permanent condition, but this concept requires
approval by the UPRR and BNSF. Additional struts may also be required, depending on the number
and size of the bridges that are constructed. For the baseline alternative,it is likely that a strut at
mid-distance between the UPRR and BNSF bridge would be required. For the full buildout
alternative, the railroad and access road bridges may provide sufficient bracing without additional
struts.
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South 180th Street Grade Separation 21 August 1999
Secant pile tip elevation at the abutment walls is determined by either the maximum vertical load
capacity and/or depth of embedment required to prevent"kickout"during excavation. For the depth
of excavation proposed, a second temporary brace is anticipated at approximately 24 feet below the
bridge girders.
Transverse seismic loads will be transferred in the plane of the secant pile wall. Longitudinal
seismic loads will be transferred as axial loads in the girders(and additional struts,if required)
through elastomeric bearing pads to the backwalls of the pile caps. The backwalls and pile caps will
transfer longitudinal loads to the soils behind them.
The center pier consists of a secant pile wall foundation,pile cap,columns and crossbeam as shown
in Figure 24. Maximum gravity loads and the allowable vertical load capacities presented in the
Draft Geotechnical Engineering Report were used to determine the length of the secant pile wall.
The length of the secant pile wall needed to support the center pier loads directly affects the
construction sequence and costs for the different bridge alternatives. Figures 24 through 31
illustrate center pier substructure configurations for various bridge alternatives,i.e.,varying the
number of tracks and adding the access road bridge. A shorthand code to identify the track and
access road configurations was developed as follows:
"Alternative XYZ"where X=number of UPRR tracks
Y= 0 if no access road bridge, 1 if an access road bridge
Z= number of BNSF tracks.
For example, as shown in Figure 30"Alternative 214"designates the full buildout alternative with
two UPRR tracks,the access road bridge, and four BNSF tracks.
4.3.5 Railroad and Access Road Bridges Construction Sequence
The general construction sequence for the railroad bridges is described below. The access road
bridge construction sequence would be similar. This sequence fits into the overall construction
sequencing described in the Project Construction Sequence in Section 7 of the report. Some details
may change, depending on the configuration, location, and number of tracks that need to be
supported.
1. Construct shoofly tracks and shift train traffic to shooflies. Install shoring parallel to the
shoofly tracks. For the baseline alternative, a maximum of three shoofly tracks can be
constructed while maintaining all required construction clearances (Figure 25).
2. Construct secant pile walls at the abutments and center pier.
■ At the abutments,the top of piles is at the bottom of the pile cap, about 8 feet below
existing ground.
■ At the center pier, construct the primary piles, filling the lower portion of the shaft with
lean concrete and above the bottom of the pile cap with either lean concrete or sand.
Construct the secondary piles using Class 4000P concrete up to the bottom of the pile cap.
Vertical pile reinforcing for secondary piles will extend up into the pile cap.
3. Excavate at abutments and construct the abutment wall pile cap.
4. For the center pier, either excavate and dewater locally,or excavate and place a tremie seal
and dewater. Construct the pile cap, columns, and crossbeam.
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South 180th Street Grade Separation 22 August 1999
5. Erect girders.
6. Place an initial 6 inches of ballast and construct new tracks across the bridge.
7. Shift the shoofly tracks and move train traffic to the new permanent alignments.
8. Remove shoring,complete the excavation of the underpass, and construct roadway underpass.
4.4 RAILROAD SHOOFLY AND TRACK REALIGNMENT
To provide a safe work zone for construction of the railroad bridges and maintain railroad
operations, a shoofly detour for each railroad track will be constructed. Figures 7 to 10 illustrates
the sequencing and extents of the proposed alignments for the railroad track work.
At the time construction begins,it is anticipated that there will be three BNSF tracks in operation.
The additional third track is planned as part of the Sound Transit Commuter Rail Project. Plans for
the BNSF shoofly alignment are based on preliminary plans for the Commuter Rail Project. Those
plans show the existing westerly BNSF track remaining along its existing alignment,the existing
easterly track realigned at 15 feet to the east of the westerly track and the new track located another
15 feet east of that track.
The first phase of construction begins with the construction of three BNSF shoofly tracks to the west
of the existing tracks(Figure 7). The BNSF shoofly extends approximately 1,100 feet north and
1,100 feet south of the South 180th Street alignment. A design speed of 45 mph,which corresponds
to the speeds shown on the BNSF track charts, was used for the layout. "Cut and throw"
construction would be used to minimize disruption to the railroad operations. In this approach, all
shoofly track work except the links to the existing tracks at the north and south end are constructed
first. This work is completed without interrupting railroad operations. After the rest of the shoofly
is ready for operation,the existing track at these north and south links is cut and the new short
track lengths constructed to connect to the shoofly. It is anticipated that the service outage times
will be limited to one eight-hour work window for each cut-over or sequence of work.
After the BNSF train traffic is shifted to the shoofly, the BNSF bridge across South 180th Street is
constructed. The tracks are installed across the bridge and the cut and throw approach is used to
shift the train operations back to the bridge alignment(Figure 8).
The UPRR shoofly construction and realignment sequencing is similar to the BNSF, as shown in
Figures 9 and 10. A shoofly will be constructed east of the existing UPRR track, train traffic will be
shifted to the shoofly so the bridge can be constructed, and finally the track will be realigned across
the bridge and train traffic shifted to it. The UPRR shoofly will re-use a segment of the BNSF
shoofly. The layout of the shoofly was based on a 45 mph design speed. The UPRR shoofly extends
approximately 1,600 feet north and 1,000 feet south of the South 180th Street alignment.
Railroad forces will do track construction above the sub-ballast. Hence, scheduling and coordination
of the shoofly construction and realignment of the tracks will be an important consideration.
An existing signal at the grade crossing will be removed as part of this project.
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South 180th Street Grade Separation 23 August 1999
The following design criteria was established with the assistance of the BNSF and UPRR for the
shoofly(detour)tracks:
Design Speed: 45mph
Degree of Curve:
Desirable: 1°00'
Maximum: 3°00'
Spiral Lengths: 70 ft minimum
Superelevation: 1.25"maximum
Track Materials: Per BNSF and/or UPRR Standards
Turnouts:
No. 9s: Per BNSF Standards
No. 10s: Per UPR.R,Standards
Rail:
133 lb. CWR Per UPRR Standards
136 lb. CWR Per BNSF Standards
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South 180th Street Grade Separation 24 August 1999
5.0 PROJECT AESTHETICS
5.1 LANDSCAPING
Due to the urban conditions and confined space,there is a very limited amount of area for proposed
landscaping. The most likely location for plantings along the corridor is between the secant piles or
back of sidewalk and adjacent properties. One area is between Building Nos. 7210 and 7212 and the
proposed roadway. It is likely that this area will be greatly disturbed during construction and would
provide a suitable location for plantings. The same is true for the area in front of the public storage
facility. However, care must taken in the plant selection and layout. It is important that the plant
root system does not expand in such a way as to interfere with the retaining wall or adjacent
utilities.
5.2 ARCHITECTURAL TREATMENTS
The major architectural feature for this project is the fascia for the secant pile walls. See Section 4.4
for a detailed discussion of the facade. The only other major element with an architectural aspect is
the Interurban Trail bridge. The use of a prefabricated steel truss, as described earlier,will provide
an aesthetically pleasing bridge.
5.3 ILLUNIINATION
In accordance with City of Tukwila standards,roadway lighting will be required for this project.
Outside the limits of the secant piles and tremie seal, standard roadway lighting will be installed.
As the roadway approaches and passes under the bridges, conventional illumination cannot be used.
Within the retaining wall area a lighting system similar to those found in tunnels will be needed.
This will likely include surface-mounted fixtures attached to the pile caps or fascia along the length
of both walls. No lighting can be attached to the bridge structures per railroad design criteria.
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South 180th Street Grade Separation 25 August 1999
6.0 TRAFFIC CONTROL
6.1 DETOURS
Several roadway detour options were investigated in this phase of the project. It was concluded,
based upon safety and cost,that South 180th Street should be closed to through traffic during
construction. To accommodate the large amount of east-west traffic displaced, a detour route will be
established to South 196th Street. Currently, South 196th Street does not cross the railroad
corridor. However, a project similar to this one is in the PS&E design phase and construction is
expected to begin in 2000. This will require that the South 180th Street project begin after South
196th Street construction is complete, approximately early 2001. The detour will include all
necessary signage,barricades, and possibly flashing message boards required to ensure a fluid flow
of traffic. Additionally,the change in traffic patterns may require adjustments to the existing signal
timings. The intersections of SR 181 and South 180th Street,SR 181 and South 196th Street, and
South 196th Street and 84th Avenue South may have to be retimed. The extent to which the detour
will affect the existing traffic and signals will be determined in the PS&E phase of the project.
6.2 ACCESS DURING CONSTRUCTION
The biggest issues in terms of restricted access due to construction are the driveways for Building
Nos. 7210 and 7212, and the public storage facility. In order to maintain accessibility to these
facilities, their relocated drives must be constructed in the initial construction phases of the project.
All other properties adjacent to the corridor will maintain access through existing or alternative
drives. Section 3.8 includes a detailed description of the proposed driveways.
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South 180th Street Grade Separation 26 August 1999
7.0 SCHEDULE
7.1 PROJECT SCHEDULE
As outlined in Section 2.2,the overall project will consist of three distinct phases. Figure 32 outlines
a preliminary schedule with various critical milestones highlighted. Phase 1 of the project will
consist of the preliminary design. The culmination of this phase will be the final acceptance of the
design report. It is expected that the submission of the final design report will be completed in mid-
August 1999. At that time it is likely that the funding options for the alternatives as discussed in
Sections 1.6 and 9 will be explored. The ultimate configuration(number of tracks, access road, etc.)
must be determined prior to the next phase.
Phase 2 consists of the preparation of the final design (PS&E),advertisement, and awarding of the
construction contract of the project. The phase will begin with a detailed subsurface investigation as
described in Sections 2.3.5 and 3.12. This will finalize the design groundwater elevations and soil
conditions. Submissions will be made at the 60 and 90 percent stages leading to the final 100
percent PS&E. The advertisement,bidding, and award of the construction of the project will follow.
It is expected this will take place in the late summer of 2000. It is important that the project be bid
and awarded as soon as possible. The main reason for this is because the beginning of construction
is based entirely on the completion of the South 196th Street. See Section 6.1 for a discussion of the
project's detour. Currently,the completion is scheduled for December 2000. However,if that project
finishes earlier, a contractor should be in place to begin the South 180th Street reconstruction.
Phase 3 of the project will consist of the construction administration and engineering. An estimated
construction schedule of 9 or 10 months will result in competition of the South 180th Street
reconstruction in late summer/early fall of 2001. The following section contains a detailed
description of the construction schedule and sequencing.
7.2 CONSTRUCTION SCHEDULE
The main objective of the construction sequencing is to maintain the operation of several"systems"
during construction of the grade separation. These include access to facilities, continuous operation
of public and private utilities, and most importantly minimal disruption to train traffic. Figure 33
shows a schematic representation of the major project elements and a detailed sequencing of
construction. Below is a consolidated description of construction phasing. Please note that the
phase numbers below do not correspond the sequencing on Figure 33.
Phase I
The initial phase will include work that can be described as"prep work." This includes removal of
existing structures, construction of the accesses described in Section 6.2, and all necessary
temporary utilities. Most of this prep work can occur without disruption to traffic on South 180th
Street and could theoretically begin right after the award of the contract.
Phase II
After completion of the South 196th Street construction,the detour can be put into place and
construction within the roadway can begin. In order to relocate the fuel and telecommunications
lines,the Interurban Trail bridge must be constructed. The relatively close proximity of the existing
fuel line will require great care in the construction of the secant pile abutments. The utilities will be
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South 180th Street Grade Separation 27 August 1999
relocated to the bridge after it has been built. The secant piles between the existing tracks will also
be constructed in this phase.
Phase III
This phase will begin the major construction elements of the project. A temporary three-track
shoofly will first be constructed between the existing tracks for the BNSF trains. With the trains on
the detour,the BNSF bridge abutments and superstructure can be constructed. Upon completion of
the bridge,the trains will be shifted to their ultimate location. See Section 4.3.5 for more details.
Phase IV
Using one of the tracks from the existing shoofly,the UPRR trains will be diverted. As in the
previous phase,this will allow for construction of the UPRR bridge foundation and superstructure.
The trains are then relocated to their ultimate location on the new bridge.
Phase V
With the train traffic on the new bridges,the majority of the roadway construction will commence.
The most difficult element of this phase will be the excavation of the roadway underneath the
bridges. This might require some specialized equipment. After excavation is complete, the tremie
(see Section 3.9)must be placed. To ensure that the seal is as tight as possible, the tremie should be
placed in the largest sections allowable. By limiting the number of joints,the possibility of
groundwater infiltrating the roadway bed is greatly reduced.
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8.0 ENVIRONMENTAL CONSIDERATIONS
8.1 STREAMS
Two riparian corridors traverse the study area.
■ Springbrook Creek flows northeast in the eastern portion of the project study area. Along the
south side of South 180th Street,the stream channel is positioned between the newly
constructed storage facility and the Springbrook Business Park. On the north side of South
180th Street, the stream channel is positioned between the proposed Oaksdale Business Park
site and an undeveloped parcel to the south of the creek channel. Riparian-associated wetland
areas are interspersed throughout the riparian corridor and were not included in the wetland
delineation study for this project.
■ Mill Creek, a tributary to Springbrook Creek,enters the study area from the south between the
BNSF and the UPRR tracks just north (downstream)of River Mile 4 of Springbrook Creek.
From the study area boundary,the stream flows approximately 990 feet to its confluence with
Springbrook Creek. Riparian-associated wetlands run nearly continuously on both sides of the
stream channel within the Mill Creek floodplain east of the railroad tracks. West of the tracks,
the stream channel becomes abruptly channeled with steep stream banks and very few riparian
wetland patches within the study area boundaries. These riparian wetlands were not included
in the wetland delineation study for this project.
Approximately 450 feet of Springbrook Creek was evaluated south of 180th Street and
approximately 830 feet of Mill Creek from its confluence with Springbrook Creek to 200 feet south of
the BNSF bridge.
Impacts to Mill Creek will occur as a result of widening the BNSF bridge over the creek. A
temporary railroad bridge extension over Mill Creek will be constructed to provide stream crossing
for three shooflies. The temporary bridge area of disturbance will be approximately 90 feet long by
30 feet wide. No in-stream work below the ordinary high water mark is proposed. Small pilings will
be driven into the streambank within the 50-foot stream buffer to support the bridge deck.
The City of Kent, regulates development activities adjacent to streams through the Kent City Code
(Section 15). The City of Kent classifies Springbrook and Mill creeks as major creeks. The code
requires that all major and minor creeks and their associated buffers in the city,where they flow on
or across undeveloped land, shall be retained in their natural state and location. Setbacks from
major creeks are within 50 feet of undisturbed vegetation.
Details of the stream survey are discussed under separate cover in the Draft Stream Study.
8.2 WETLANDS
There are six wetlands within the study area boundaries.
■ Wetland A is located in Tukwila on the north side of South 180th Street within a wide swale that
runs north/south between the UPRR ROW and the Interurban Trail and extends north beyond
the studv area. The total area of Wetland B is estimated to be greater than 1 acre.
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South 180th Street Grade Separation 29 August 1999
■ Wetland B is located in Tukwila on the north side of South 180th Street within a wide swale that
runs north/south between the BNSF and UPRR ROWS and extends north beyond the study area
boundaries. The total area of Wetland A is estimated to be greater than 1 acre.
■ Herrera Wetland A is located in Renton in the southwest corner of the parcel located east of the
BNSF and north of South 180th Street. The area of this wetland was estimated to be
approximately 0.25 acre in size within the study area.
■ Herrera Wetland B is located in Renton and is part of a large wetland system that extends north
beyond the study area,where it encompasses shrub/scrub,emergent and open water vegetation
classes that are hydrologically connected to Springbrook Creek. The area of the wetland was
estimated to be approximately 0.25 acre within the study area.
■ Wetland C is located in Kent on the south side of South 180th Street within a depression that
runs north/south between the BNSF and UPRR ROWS. The total area of Wetland C is estimated
to be 722 square feet.
■ Wetland D is located in Tukwila on the north side of South 180th Street within a wide swale that
runs north/south between the Interurban Trail and the commercial/industrial properties beyond
the western boundary of the study area. The total area of Wetland D is estimated to be greater
than 1 acre.
A total of 1.11 acres of wetlands will be filled and 2.3 acres of wetland buffer will be filled as a result
of the development of three shooflies for the BNSF and UPRR tracks. No impacts to wetlands are
expected to occur as a result of the roadway and underpass construction.
In order to achieve the City of Tukwila's goal of no net loss of wetland functions and acreage,
alteration of wetlands require the applicant to provide a restoration, enhancement, or creation plan
to compensate for the wetland impacts at a ratio of 1.5 to 1 (area created:area impacted).
The objective of the mitigation plan, developed for the project,would be to create a mitigation
wetland with several habitat types to compensate for the lost functions and values of Wetland C and
the filled portions of Wetland A and its buffer that provide connectivity to existing habitat corridors.
The created wetland would be consistent with mitigation requirements as stated in the Tukwila
Municipal Code by providing a minimum of a 1.5 to 1 replacement ratio for wetland areas.
Three potential wetland mitigation sites were investigated and are discussed below.
A. Herrera Wetlands Site
The Herrera Wetlands site is a parcel located within Renton east of the BNSF and north of
South 180th Street. The estimated available upland area for mitigation at this site is 2.15
acres.
Given the current dominance of blackberry throughout this area, significant improvement in
vegetation community structure and diversity is achievable. Significant improvement in
wildlife habitat can also be achieved with connectivity to existing study area wetlands and the
Springbrook riparian corridor.
The site is within the jurisdiction of the City of Renton,therefore, an agreement would need to
be established between the City of Tukwila and the City of Renton for use of the site.
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South 180th Street Grade Separation 30 August 1999
B. Mill Creek Upland Site
The Mill Creek upland site is a"landlocked"parcel positioned south and east of Mill Creek and
immediately east of the BNSF ROW within Kent. The parcel comprises approximately 8.4
acres. Topographically,the parcel is positioned approximately 20 feet above the elevation of
Mill Creek and its associated riparian wetlands.
The potential wetland creation area is located in what appears to be an upland area dominated
by a large blackberry thicket in the western portion of the site east of the railroad tracks.
Prior to consideration of this site for wetland creation, subsurface hydrologic characteristics
would need to be documented and groundwater elevations determined through a wetland
reconnaissance of the property during the growing season. Given the current dominance of
blackberry throughout this area, significant improvement in vegetation community structure
and diversity is achievable. Significant improvement in wildlife habitat can also be achieved
that can be linked directly to the greater Mill Creek/Springbrook Creek riparian habitat
corridor.
This parcel is located within Kent,therefore,purchase of the property by the City of Tukwila
or an agreement between the two cities would need to be established for development of the
parcel as a wetland mitigation site.
C. City of Tukwila Wetland WL12 Mitigation Site
The Wetland 12 site is located to the north of South 180th Street and west of the UPRR tracks
and the Interurban Trail. An existing mitigation area is located on the south side of this
wetland immediately beyond the study area boundary on a privately owned parcel. A portion
of this area is currently undeveloped and may be available for wetland creation immediately
adjacent to the existing wetland mitigation area. A determination of the acreage available for
mitigation would need to be determined through site reconnaissance with permission from the
property owner.
Significant increase in wetland functions could be achieved by introducing shrub-scrub and
forested vegetation community structure into the existing mitigation area that is consistent
with other vegetation community patches within Wetland 12. Improvement in wildlife habitat
can also be achieved that can be linked to the existing wetland and to the wetlands on the east
side of the Interurban Trail. One benefit of utilizing this site is that compensatory mitigation
for the impacted portions of Wetland A and Wetland C could potentially be achieved within the
City of Tukwila's jurisdictional boundary.
Detailed wetland descriptions are described in the South 180th Street Grade Separation
Wetland Study under separate cover.
8.3 WILDLIFE
The South 180th Street Grade Separation project contains no threatened or endangered species;
however, it does contain wetlands and riparian corridors, which are areas considered priority
habitats in King County. Vegetation communities that serve as wildlife habitat within the project
study area include the following.
■ Scrub-shrub wetland areas dominated by willows and open water between the BNSF and UPRR
tracks and between the UPRR tracks and the Interurban Trail, on the northern side of the
roadway
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South 180th Street Grade Separation 31 August 1999
■ Blackberry thickets along the Interurban Trail along both sides of the roadway and in the
southern half of the undeveloped site on the northern side of the roadway, adjacent to the BNSF
railroad tracks
■ Weed and reed-canary grass-dominated areas on the south side of the roadway between the
BNSF and UPRR tracks
■ A small forested area dominated by bigleaf maple within the northwestern portion of the
remediation site; and a small forested area with bigleaf maple and locust south of the Public
Storage site
■ A willow-dominated corridor adjacent to Springbrook Creek on both sides of the roadway.
Impacts to wildlife habitat would consist of the loss of approximately 1.11 acres of scrub-shrub and
open water wetlands between the UPRR and BNSF tracks. This loss of wildlife habitat would be
compensated by wetland creation in areas adjacent to existing wetlands and wildlife habitat areas.
Details of a wildlife survey and habitat assessment are discussed under separate cover in the Draft
Wildlife Study.
8.4 WATER QUALITY
Water quality is considered degraded in the lower reaches of Springbrook and Mill Creeks. Nonpoint
source pollution occurs throughout the watershed. The Western Processing site on Mill Creek
upstream of the study area near South 196th Street in Kent may be considered a potential nonpoint
source of pollution. The site has been designated as an EPA Superfund site and will be cleaned up
over several years. Recent data have documented high levels of zinc and cadmium contamination in
sediments in Mill Creek(R.W. Beck&Associates, Inc., 1997).
During the summer of 1994, a U.S. Geological Survey(USGS)stream monitoring gauge was
installed on Mill Creek about 600 feet upstream of the Springbrook Creek confluence, between the
train trestles. The gauge records water temperature, specific conductivity, dissolved oxygen, pH, and
water elevations every 15 minutes. Available records covering the period between September 16 and
December 22, 1994 were compared with the requirements of adult salmon that were actively
migrating during this time period (Harza Northwest, Inc., 1995). Harza Northwest reported
standards were exceeded for turbidity, as well as acute and chronic toxicity criteria for lead and
chromium. Low levels of phthalate esters and polycyclic aromatic hydrocarbons were also found. Of
the standards that have been exceeded in Springbrook Creek, phosphorus, dissolved oxygen,
turbidity, and fecal coliform bacteria consistently do not meet DOE water quality standards or
guidelines (R.W. Beck & Associates, Inc., 1997). Fish mortality may occur from chronic exposure to
concentrations of other metals that exist at levels lower than the acute levels because of synergistic
affects experienced by fish when exposed to high levels of more that one metal or other water quality
problems. These factors, especially when the synergistic affects are considered, likely cause changes
in fish distribution within the watershed, poor growth and survival, and direct mortality to salmonid
populations (Harza Northwest, 1995).
The Washington State Department of Ecology (DOE)has established numerical standards for
specific water quality parameters in part to protect fish and wildlife resources. In compliance with
Section 303(d) of the Clean Water Act, DOE has listed Springbrook Creek as not meeting state
surface water quality standards for fecal coliform, temperature, dissolved oxygen, cadmium, copper,
mercury, and zinc. Sampling along Springbrook Creek channel suggests that total petroleum
hydrocarbons (TPH)concentrations exceed soil cleanup levels, thus requiring treatment(i.e., on-site
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South 180th Street Grade Separation 32 August 1999
bioremediation)or restricting disposal of these sediments,if dredged,to an approved landfill (R.W.
Beck&Associates,Inc., 1997). Dissolved oxygen sample sites in Mill Creek have often been less
than optimum,whereas levels below the lethal limit for salmonids have been documented in the
lower gradient reaches of Springbrook and Mill Creeks(Harza Northwest, 1995). Some of the low
dissolved oxygen levels may be due to influx of low-oxygen groundwater,lack of gradient,low flow
velocities,lack of in-stream structures(i.e.,woody debris),and lack of riparian vegetation cover
(R.W. Beck&Associates, Inc., 1997). Additional data can be found in the Draft Stream Study.
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South 180th Street Grade Separation 33 August 1999
9.0 PROJECT COSTS
A detailed breakdown of the preliminary construction cost estimate is included in Appendix A. The
construction cost estimate for the preferred alternative is approximately$15.6 million. The estimate
is based upon current construction costs adjusted to an assumed start in the year 2000. All utility
replacement and relocation costs,except for drainage,will be the responsibility of the owners. This
baseline cost estimate is based upon the following:
■ Four lane roadway underpass with center turning lane
■ Bridge for Interurban Trail
■ One-track bridge for UPRR
■ Two-track bridge for BNSF
As shown in the estimate,the tremie seal and retaining wall are among the most costly items for the
project. They also are the most variable due to the additional subsurface investigation to be
performed. The findings could have an impact on the current design. A lower existing groundwater
(or the ability to lower during construction)will greatly reduce the size and cost of the tremie seal,
see Section 3.9. The secant pile walls were based upon a limited subsurface soil exploration. If
conditions are found to be other than those assumed,the depth of the piles will either lengthen or
shorten. This will also impact the current construction cost estimate.
Several additive alternatives have been identified for the project. These options include the addition
of tracks and an access road to the current configuration. Additional costs with contingencies for
these options are presented in the following. Refer to Appendix A for detail. The likelihood of these
alternatives are dependent upon the possibility of additional funds being contributed by various
stakeholders.
Alternative A—One additional UPRR track on bridge.
Foundation and substructure only - $124,000
Superstructure - $116,100
Total $240,000
Alternative B—One additional BNSF track on bridge.
Foundation and substructure only- $106,000
Superstructure - 85,000
Total $191,000
Alternative C —Two additional BNSF tracks on bridge.
Foundation and substructure only- $208,000
Superstructure - $154,000
Total $362,250
Alternative D—Access road bridge.
Foundation and substructure only- $ 78,000
Superstructure - 94,000
Total $172,000
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South 180th Street Grade Separation 34 August 1999
10.0 PUBLIC INVOLVEMENT
An open House for the South 180th Street Grade Separation project was organized and held on 18
February 1999 at the City of Tukwila City Hall Council Chambers from 4:30 p.m. to 6:30 p.m. The
open house was organized to present to the public the three key issues that defined this project.
These issues included the following.
■ Issue No. 1: Should the realignment of South 180th Street go over the railroads or go under the
railroads?
■ Issue No. 2: Should the City maintain four lanes for traffic or expand the corridor to
accommodate six lanes of traffic?
■ Issue No. 3: Should a detour be provided in the vicinity of the South 180th Street project or
should the City rely on"existing"corridors to accommodate closing South 180th Street for
construction?
Those attending the public open house were presented with various facts regarding each of these
issues. The facts associated with each of these issues is presented below.
Issue No. 1—Grade Separating South 180th by Going Over the BNSF and UPRR
■ Significant impacts to adjacent properties in terms of driveway access
■ Higher overall project costs(exceeds the proposed project budget by several million dollars)
■ No required temporary (shoofly) railroad realignment
■ Minimizing impacts to the railroads and coordination during construction
• Some Springbrook Creek environmental impacts
■ Significant visual impacts to the area
■ Project limits will extend from West Valley Highway to beyond Springbrook Creek Crossing
Going Under the BNSF and UPRR
■ Minimizing impacts to adjacent properties and maintaining access to nearly all properties
■ Costs are near the proposed project budget
• A temporary (shoofly) railroad realignment is required with significant impacts to the railroads
and coordination during construction
■ Minor impacts to Springbrook Creek; Impacts to the wetlands along the railroad right-of-way
will require permits and mitigation
■ Roadwav reconstruction limits are minimized (72nd Avenue South to Springbrook Creek
crossing)
The public consensus regarding this issue from written comments received were the following.
■ 0 percent favored a grade separation going over the railroads
■ 100 percent favored a grade separation going under the railroads
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South 180th Street Grade Separation 35 August 1999
Issue No.2—Maintaining the Existing Four Lanes of Traffic will
■ Maintain project budget
■ Add some capacity to this segment of roadway. The grade separation eliminates the current
delays associated with the trains.
■ Still require additional arterial crossings to meet future traffic volume projections
■ Still require other improvements. The intersections will limit the improvement of added
capacity. The intersections level of service will ultimately control the flow of traffic.
■ Not require additional ROW.
Providing Six Lanes for Traffic will
■ Not meet the traffic volume projections. Additional arterial crossings are still necessary to meet
future traffic volumes
■ Still require other improvements. Intersections will limit the improved added capacity(two new
lanes). The intersections level of service will ultimately control the flow of traffic.
■ Add more cost to the project. Project budget will be exceeded with addition of lanes.
• Extend the project limits to West Valley Highway and to 80th Avenue South resulting in more
impacts to adjacent property. Additional Right-of-way will be required.
The Public consensus regarding this issue from written comments received were
100 percent favored maintaining four lanes along South 180th Street
0 percent favored expanding South 180th Street to six lanes
Issue No. 3—Detouring South 180th Street by Building a Temporary South 180th Street
Connection will
■ Significantly add project costs associated with this temporary connection
■ Add significant impacts (temporary and permanent)to all the adjacent properties
■ Allow construction to begin in Year 2000
■ Require a construction schedule estimated at 18 months
■ Will require an at-grade railroad crossing to remain in service during construction
■ Cause traffic delays associated with the construction work adjacent to the detour
• Add more impacts to existing wetlands and Springbrook Creek
Using South 196th Street as the Eventual Signed Detour Route will
■ Delav the start of construction of South 180th Street until 2001 (South 196th Street is scheduled
to be completed and opened in late 2000)
■ Minimize property and environmental impacts along South 180th Street
■ Allow the project budget to be maintained
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South 180th Street Grade Separation 36 August 1999
■ Minimize detour requirements and costs to temporary signing and maintenance during
construction
■ Reduce the estimated construction schedule to approximately 9 or 10 months
■ Remove the existing South 180th Street at-grade railroad crossing as soon as construction begins
in 2001.
The public consensus regarding this issue from written comments received were
0 percent favored building a temporary detour for South 180th Street
100 percent favored waiting and using the South 196th Street as a temporary detour
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South 180th Street Grade Separation 37 August 1999
11.0 RECOMN ENDATION AND ENDORSEMENT
The preferred alternative as described in the previous sections consists of an underpass beneath the
railroads,four lanes of traffic with a center turn lane, an Interurban Trail bridge, a one-track UPRR
bridge, and a two-track BNSF bridge. The shared access road bridge is not included. Based on
engineering analysis,this is the preferred alternative because it meets the following project goals:
1. Safety improvements to the corridor for vehicular and train traffic.
2. Increase in traffic flow and decrease in delays.
3. Adherence to strict budget.
During review of the Draft Design Report,both the UPRR and BNSF stated that they would like to
have the project designed and constructed for a two-track UPRR bridge, a four-track BNSF bridge
and a shared access road bridge. It was understood by both railroads that the added costs for
widening the bridges and for the access road bridge would need to be paid by the railroads, although
no financial agreement had been worked out as of mid-August 1999.
Based on all the above, the recommended alternative for Phase 2 final design is as follows.
■ An underpass beneath the railroads
■ A four-lane South 180th Street with a center turn lane/median
■ An Interurban Trail bridge
■ A two-track UPRR bridge
■ A four-track BNSF bridge
■ A shared access road bridge
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South 180th Street Grade Separation 38 August 1999