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TECHNICAL MEMORANDUM
Project: Kennydale Gateway
4350 Lake Washington Boulevard N, Renton, WA
Subject: Transportation Impact Analysis – REVISED
Date: June 14, 2021
Author: Marni Heffron, P.E., P.T.O.E.
This memorandum presents the transportation analysis for the Kennydale Gateway project located at 4350 Lake Washington Boulevard N in Renton, WA. This analysis was performed to be consistent with the City of Renton’s Traffic Impact Analysis Policy Guidelines for New Development.1 It includes a project description, estimate of project-generated trips, analysis of future traffic conditions in the site vicinity, and assessment of potential mitigation. This memorandum has been revised for the current development proposal and supersedes the analysis of this project dated September 9, 2019.2 As described in detail below, the project site is adjacent to the Interstate 405 (I-405) / NE 44th Street interchange, where the Washington State Department of Transportation (WSDOT) and Sound Transit will be constructing major improvements. WSDOT has performed extensive analysis of the interchange
and nearby intersections and evaluated future 2025 and 2045 conditions. These future conditions had assumed more intensive development of the project site than is now contemplated. This transportation analysis presents trip generation estimates for the proposed development, and compares that to WSDOT’s analysis assumptions. Information about planned improvements is also provided. Per guidance from the City of Renton,3 intersections beyond the interchange area were not studied.
1. Introduction and Project Description
The 7.7-acre project site is bounded by Lake Washington Boulevard N on the west and north and I-405 and the southbound on-ramp to the east. The south edge of the site is a wooded public access corridor along the May Creek Trail.
The project proposes to develop three four-story residential buildings with a total of up to 390 apartment units (the current site plan includes 375 units, but the higher number was used as a worst-cast for this analysis) and parking for about 400 vehicles—about half in surface lots and about half in structure on
the first levels of the three buildings. One of the buildings (Building 1) would also include a 1,500 square foot ground-floor (sf) commercial retail space near the development’s entrance on Lake Washington Boulevard N. It is noted that the previous analysis of this site in September 2019 assumed
that Sound Transit would construct a 200-space park-and-ride lot at the north end of the site. The park-and-ride lot is now proposed to be constructed elsewhere, likely on the east side of I-405. The site plan is shown on Figure 1.
1 Provided by M. Herrera – City of Renton, October 8, 2020. 2 Heffron Transportation, Inc., Kennydale Gateway Transportation Analysis, September 9, 2019. 3 Pre-application meeting, February 2019.
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Figure 1. Kennydale Gateway Site Plan
Source: HLR Architects, June 10, 2021.
2. Future Transportation Improvements
WSDOT is planning major improvements as part of the I-405, Tukwila to I-90 Vicinity Express Toll
Lanes Project (Tukwila to I-90 Project). In general, WSDOT’s project proposes to add one lane to I-405 in each direction for about nine miles beginning near State Route (SR) 167 and continuing approximately one mile north of Interstate 90 (I-90). The project would also add a general purpose
(auxiliary) lane to southbound I-405 between milepost (MP) 6.7 (north of N 30th Street) and MP 7.1 (south of NE 44th Street) and from MP 9.4 (north of 112th Avenue SE) to MP 10.5 (north of Coal Creek Parkway). The existing high-occupancy vehicle (HOV) lane on I-405 and the additional auxiliary lane
would be operated as a two-lane express toll lane system.4 4 WSDOT, Transportation Discipline Report: I-405, Tukwila to I-90 Vicinity Express Toll Lanes Project (MP 0.0 to 11.9) and Downtown Bellevue Vicinity Express Toll Lanes Project (MP 11.9 to 14.6), July 2018.
N
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WSDOT also proposes to rebuild the I-405 / NE 44th Street interchange. The current plan proposes to relocate NE 44th Street / Lake Washington Boulevard N to pass under I-405. On the west side of I-405,
regrading would begin at about N 43rd Street, and the grade of the street at Seahawk’s Way would be lowered by about 7 feet compared to the current overpass condition. In addition, Sound Transit plans to locate a new Bus Rapid Transit station at the interchange, which would be accessed via HOV-only ramps from the center lanes of I-405. Figure 2 shows a concept of the interchange, which includes the following features:
• The northbound ramps, southbound ramps, and direct HOV ramps would be controlled by roundabouts where they intersect Lake Washington Boulevard N and NE 44th Street. WSDOT’s
Transportation Discipline Report for the corridor evaluated these three intersections,
• The WSDOT analysis also contemplated that the intersection at the Lake Washington Boulevard N / N 43rd Street intersection, at which a new east leg would serve as the Site access for the Kennydale Gateway project, would be controlled with a roundabout that would be built by others. The proposed project proposes to construct this roundabout.
• The intersection at Lake Washington Boulevard N / Seahawks Way would be reconfigured to prohibit all left turn movements. Turns from Seahawks Way would be stop-sign controlled. Prohibited movements would proceed to adjacent roundabouts to reverse direction.5 It is noted that WSDOT had originally assumed that the site would have a secondary access connecting to the south leg of the Seahawks Way intersection. However, that access is not proposed by the project.
Figure 2. Concept Plan for Future I-405 / NE 44th Street Interchange
Source: WSDOT and Flatiron Lane, July 2020. Sound Transit is helping to fund some of the improvements along the I-405 corridor and at the NE 44th Street interchange to support its voter-approved Bus Rapid Transit (BRT) corridor, known as Stride. The S1 line between Burien and Bellevue is currently anticipated to begin operating in 2024.6 The improvements include the 44th Street Station and a 200-space park-and-ride lot near the interchange.
WSDOT’s plan and analysis of the interchange had assumed that the 200-space park-and-ride lot would be constructed at the Kennydale Gateway site, but Sound Transit is now proposing that the park-and-ride be located elsewhere, likely on the east side of I-405.
Because the WSDOT and Sound Transit improvements are funded, all analyses herein reflect their completion for future conditions. No analysis of the existing roadway system was performed.
5 Based on geometric and traffic control assumptions in WSDOT’s Synchro model for this intersection, HNTB, filename: 2025Build.AM.syn, October 2016. 6 Sound Transit website: https://www.soundtransit.org/system-expansion/i-405-brt, accessed April 6, 2021.
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3. Site Trip Generation
Trip generation for the Kennydale Gateway project was estimated using rates published in the Institute of Transportation Engineers’ (ITE) Trip Generation Manual7 and adjusted to reflect potential non-vehicular modes of travel and internal trips among the uses. The following describes the assumptions for each of the land uses.
• Apartments – Trips were derived using equations published for Multifamily Housing (Mid-Rise)
(Land Use 221), which is appropriate for the proposed four-story residential component. It is assumed that 20% of the commute trips could be made using the planned Stride BRT service on I-405, and planned non-motorized station connections to the site. This percentage is consistent with US Census Bureau mode-of-travel surveys for residents living near the site.8 These data showed that in 2010, about 84% of all resident trips were made by vehicle (70% by single-occupant vehicle and 13.7% by carpool). Transit trips accounted for 7.2% of the resident trips. With the future BRT system, it is likely that transit use will increase. Therefore, the 80% of the trips assumed to occur by vehicle is a reasonable assumption.
• Commercial Retail – The small retail space on the site (about 1,500 sf) could accommodate different types of uses ranging from take-out food services, a coffee shop, and/or other convenience services. Trips were estimated using the averages of rates for a Coffee/Donut Shop without Drive-through Window (Land Use 936), Fast Food Restaurant without Drive-Through Window (Land Use 933), and Shopping Center (Land Use 820) land uses contained in the Trip Generation Manual. Many customers of the commercial use(s) are expected to live in the adjacent apartments and make “internal” trips within the site. Those “internal” trips would not add to the site driveways or adjacent roadways. The highest percentage of internal use is expected to occur
in the morning, if a coffee shop is located in the commercial space. The resulting trip reductions range from 50% in the PM peak hour to 75% in the AM peak hour.
The trip rates and internal-trip percentage assumptions for the site are listed in Table 1.
7 ITE, 10th Edition, September 2017. 8 U.S. Census Bureau, American Community Survey, compiled by Puget Sound Regional Council, 2014. Data reviewed for Transportation Analysis Zones (TAZ) 323 (where site is located) and TAZ 310 located to the north.
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Table 1. Trip Generation Rates, Equations, and Vehicle Trip Adjustments
Land Use / Definition Trip Generation Rates and Equations 1 Trip Reduction for Transit or Internal Trips
Multifamily Housing (Mid-rise) (ITE Land Use Code 221) – Includes apartments, townhouses, and condominiums located with the same building with at least three other dwelling units and that have between three and 10 levels (floors). Equations for a “General Urban/Suburban” setting were used.
Daily T = 5.45(X) – 1.75 (50% in, 50% out) 20% (transit)
AM Peak Hour of Adjacent Street Ln(T) = 0.98 Ln(X) – 0.98 (26% in, 74% out) 20% (transit)
PM Peak Hour of Adjacent Street Ln(T) = 0.96 Ln(X) – 0.63 (61% in, 39% out) 20% (transit)
Retail/food service (Average of rates for Coffee/Donut Shop (LU 936), Fast Food Restaurant (LU 933), and Shopping Center (LU 820) land uses) - – The small commercial use on the site is anticipated to cater to local residents. It could include a combination of uses such as take-out food services, coffee shop, dry cleaners, and/or other convenience services.
Daily 2 192.0 trips /1,000 sf (50% in, 50% out) 66% 3 (internal)
AM Peak Hour of Adjacent Street 2 42.4 trips / 1,000 sf (50% in, 50% out) 75% 3 (internal)
PM Peak Hour of Adjacent Street 2 22.8 trips / 1,000 sf (50% in 50% out) 50% 3 (internal)
1. Institute of Transportation Engineers (ITE) Trip Generation, 10th Edition, September 2017. For residential equations, T = number of
trips, X = number of dwelling units; for commercial rates, “sf” = square feet.
2. Peak hour rates are the averages of rates for the three land uses; daily rate is average of Shopping Center and Fast-Food Restaurant
rates as there is no published daily rate for Coffee/Donut Shop.
3. Estimated based on expected use patterns. Retail typically generates little morning peak hour traffic unless it is occupied by a
coffee shop, in which case, trip reduction for internal trips would be highest in the morning. Vehicle trips were estimated using the rates and equations together with the internal- and transit-trip
reduction assumptions described above. The resulting vehicle trip estimates are summarized in Table 2. As shown, the site is expected to generate an estimated 1,640 vehicle trips per day with 82 trips during the AM peak hour and 133 trips during the PM peak hour.
Table 2. Vehicle Trips Generated by Site
Daily Trips
AM Peak Hour Trips PM Peak Hour Trips
Land Use Proposed Size In Out Total In Out Total
Apartments 390 units 1,540 8 58 66 73 44 117
Retail / Food Service 1 1,500 sf 100 8 8 16 8 8 16
Total Site 1,640 16 66 82 81 52 133
Source: Heffron Transportation, Inc., June 2021. Applied trip generation rates and vehicle adjustments presented in Table 1.
1. Assumed to be commercial retail / food service and/or convenience uses.
As described in the next section, WSDOT’s analysis of interchange improvements had assumed trips associated with the Kennydale Gateway site including trips to a 200-space Sound Transit park-and-ride lot, which are described in the subsequent section. New analysis was performed to adjust the site’s
estimated trip generation to the totals listed above.
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4. Year 2025 Traffic Volumes
WSDOT, through its consultant HNTB, performed extensive analysis of the improvements at the NE 44th Street interchange. It evaluated future conditions without and with the improvements for the years 2025 and 2045. The full corridor growth assumptions were provided in the Transportation Discipline
Report: I-405, Tukwila to I-90 Vicinity Express Toll Lanes Project (MP 0.0 to 11.9) and Downtown Bellevue Vicinity Express Toll Lanes Project (MP 11.9 to 14.6).9 The detailed traffic volumes and geometric assumptions were obtained from models provided by WSDOT in both the SIDRA software files (used to evaluate roundabouts) and Synchro software files (used to evaluate the intersection at Lake Washington Boulevard N / Seahawks Way).10 The year 2025 traffic volume conditions were used to evaluate the potential impacts of the Kennydale Gateway project. The year 2025 traffic volumes with WSDOT’s proposed interchange improvements
were gleaned from the models and are shown on Figure 3 and Figure 4 for the AM and PM peak hours, respectively. Volumes west of I-405 were adjusted to account for the current Kennydale Gateway development program and the relocation of the park-and-ride lot. Volumes at the HOV ramp
intersection and those east of I-405 were left unchanged from WSDOT’s original analysis to reflect worst-case conditions.
9 WSDOT, July 2018. 10 WSDOT/HNTB Sidra and Synchro models for year 2025 build (with interchange improvement) conditions.
Project
Site
StudyArea Intersection
Future Roundabout
Future Bus Rapid Transit (BRT) StationLake Washington Blvd N405
Seahawks Way
Northbound
On-Ramp
N 43rd St
Key
HOV Ramp
40 789 2
15 193 14
62
3
0
330
0
50
1,181
X
105
222
X
10
276
52
78 1
1,133
360
89
85
35
485
45
37
13 405 13
363
264
30
45
130
445
271
292
60
561
152
95
33
28
82
83 1
722
520
1
48
415
one way
Figure 3
Year 2025 Traffic Volumes
WSDOTAnalysis with SiteAccessAdjustments
AM Peak Hour
one
way
KENNYDALE
GATEWAY
N
Project
Site
StudyArea Intersection
Future Roundabout
Future Bus Rapid Transit (BRT) StationLake Washington Blvd N405
Seahawks Way
Northbound
On-Ramp
N 43rd St
Key
HOV Ramp
70 244 2
50 538 78
49
0
3
223
1
30
516
X
345
646
X
20
260
78
217 20
505
821
90
67
36
185
53
98
10 703 10
462
123
20
70
140
700
232
372
220
402
188
35
38
66
167
174 1
401
869
1
67
115
Figure 4
Year 2025 Traffic Volumes
WSDOTAnalysis with SiteAccessAdjustments
PM Peak Hour
one way
one
way
KENNYDALE
GATEWAY
N
KENNYDALE
GATEWAY
N
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According to WSDOT,11 new traffic from three specific major developments were included in the year
2025 traffic volume forecasts at this interchange in addition to background growth:
• The Port Quendall Terminals development located on the north side of Lake Washington
Boulevard N between N 43rd Street and Seahawks Way;
• The Hawk’s Landing development located on the south side of Lake Washington Boulevard N
between the southbound I-405 on-ramp and N 43rd Street; and
• The Kennydale Mixed-Use development located on the south and east side of Lake Washington
Boulevard N.
The last development listed above is the subject site. The numbers of trips assumed to be generated by the subject site in the WSDOT analysis were derived from the traffic operations models. The WSDOT
analysis had assumed that the site would have two access driveways: the primary driveway was assumed to be a right-in/right-out only onto Lake Washington Boulevard N opposite Seahawks Way at the northwest corner of the site, a second access was assumed to connect to the proposed roundabout at
N 43rd Street. The numbers of peak hour trips assumed in WSDOT’s 2025 models are summarized in Table 3; the estimates prepared for the current proposal and described previously are included for comparison. As shown, the current proposal is expected to generate fewer trips than had already been assumed in the WSDOT analysis (241 fewer trips in the AM peak hour and 192 fewer trips in the PM peak hour). Therefore, the analysis performed by WSDOT presents a conservatively high estimate of trips and traffic operations.
Table 3. Comparison of Kennydale Gateway Site Trips to WSDOT Assumed Condition
AM Peak Hour Trips PM Peak Hour Trips
Analysis Condition In Out Total In Out Total
Assumed by WSDOT in its 2025 Models 1 167 156 323 151 174 325
Updated Estimate for Site (see Table 2) 16 66 82 81 52 133
Net Difference -151 -90 -241 -70 -122 -192
1. Determined from WSDOT / HNTB Sidra and Synchro models for year 2025 build (with interchange improvement) conditions.
5. Traffic Operations
Levels of service (LOS) for intersections at and near the NE 44th Street interchange were determined using WSDOT’s SIDRA and Synchro traffic operations models described earlier. Level of service, is a
measure of congestion, with LOS A reflecting good operations with little to no congestion and LOS F, reflecting poor operations with substantial congestion. While WSDOT had no targeted level of service standard for the I-405 corridor improvements, it did note intersections that would operate at or below
LOS E conditions. Table 4 summarizes intersection operations for year 2025 conditions, which as noted above, did account for development of the Kennydale Gateway site with more trips than expected from the current development program. Adjustments were made to the Seahawks Way and N 43rd Street intersections to remove the previously assumed secondary access for the Kennydale Gateway site at Seahawks Way. All
11 E-mail from Sean Quarrie of WSDOT to Marni Heffron, Heffron Transportation, March 8, 2019.
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access to that site is now proposed to occur at N 43rd Street. As shown, all of the proposed intersections are expected to operate at good levels of service (LOS B or better) in the year 2025 with the proposed
interchange configuration.
Table 4. Intersection Level of Service – Year 2025 conditions
With Volumes Assumed by WSDOT a
Intersection Proposed Control AM Peak Hour PM Peak Hour
Lake Wash Blvd N / N 43rd St / Site Access Roundabout B A
Lake Washington Boulevard N / Seahawks Way Stop signs on Seahawks Wy / No left turns allowed A A
NE 44th St / SB Off and On Ramps Roundabout A A
NE 44th St / HOV Ramp Roundabout A A
NE 44th St / NB Off Ramp Roundabout A A
Lake Wash Blvd N / NB On-Ramp Roundabout A A
Source: Heffron Transportation, Inc., June 2021. Year 2025 SIDRA and Synchro files provided by WSDOT were used.
a. The WSDOT assumed volumes and geometries were used for all intersections except for the Lake Washington Boulevard N
intersections with N 43rd Street / Kennydale Gateway Access and Seahawks Way intersections, which were adjusted to reflect the
current traffic volume estimates for the Kennydale Gateway site. That roundabout was also assumed to have one approach lane
on all legs. WSDOT’s Transportation Discipline Report also assessed year 2045 conditions with the proposed improvements. That analysis showed that all of the roundabouts would continue to operate at LOS A in both the AM and PM peak hour conditions. The WSDOT analysis had assumed that the stop-controlled intersection at Lake Washington Boulevard N / Seahawks Way would degrade by 2045 to LOS C in the AM peak hour and LOS B in the PM peak hour, but that analysis assumed a driveway to the park-and-ride. Without either the park-and-ride or that driveway, this intersection would also operate at LOS A in 2045.
6. Future Roundabout at Lake Washington Blvd N / N 43rd Street
WSDOT’s NE 44th Street interchange improvements contemplate a future roundabout at the Lake Washington Boulevard N / N 43rd Street / Site Access intersection to be built by others. The roundabout configuration that WSDOT assumed had two lanes on each of the major Lake Washington Boulevard N
approaches, and one lane each on the minor N 43rd Street and the Site Access approaches. As previously noted, the WSDOT analysis had assumed a 200-stall park-and-ride lot on the site with a right-in/right-out only driveway on Lake Washington Boulevard N opposite Seahawks Way. The current proposed Kennydale Gateway site plan would have neither the park-and-ride lot nor this driveway. All site-generated traffic would arrive and depart the site through the roundabout at N 43rd
Street. Because the site generated volumes and access would differ from the prior WSDOT analysis, future operations for a roundabout at Lake Washington Boulevard N / N 43rd Street / Site Access were evaluated. It was determined that a single-lane roundabout (one approach lane in all directions) would
operate at LOS B during the AM peak hour and LOS A during the PM peak hour with the proposed project. The project proposes to construct a single-lane roundabout at this intersection.
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7. Summary
The proposed Kennydale Gateway site is expected to generate an estimated 1,640 vehicle trips per day with 82 trips during the AM peak hour and 133 trips during the PM peak hour. More traffic had been assumed by WSDOT in its plans and analysis for future improvements at the NE 44th Street interchange with I-405. The substantial upgrade to this interchange, which will replace the existing freeway overpass with an under-crossing, add a direct access ramp connection to the I-405 HOV lanes, and replace ramp junction intersections with roundabouts is expected to operate very well in the future. Analysis determined that the proposed ramp intersections would operate at LOS A in the year 2025 and beyond with growth associated with the Kennydale Gateway and other local projects. The project would construct a single-lane roundabout at the Lake Washington Boulevard N / N 43rd Street / Site Access intersection. This roundabout is expected to operate at LOS B during the AM peak hour and
LOS A during the PM peak hour. No further mitigation would be needed to accommodate the project.
MCH/tsm
Kennydale Gateway Traffic Impact Analysis - REVISED - 06-14-2021.docx