HomeMy WebLinkAboutRS_Response_to_Comments_TIA_250228_v1
Wood Environment & Infrastructure Solutions, Inc.
4600 East Washington Street, Suite 600
Phoenix, Arizona 85034
T: (602) 733-6000
F: (602) 733-6100
www.woodplc.com
April 6, 2020
Wood Project No. PS19203160
To
Mr. Clark H. Close
Senior Planner
City of Renton
1055 S. Grady Way, Renton, WA 98057
Response to Comments: Flatiron-Lane JV TIA
Response to comments Prepared by: Anita S Johari, PE, PTOE, Lead Traffic Engineer, Wood.
Comment 1: The City’s Transportation Department has reviewed the Traffic Impact Analysis Report and
found that there is more analysis and information needed for the impact of the 47 vehicles per hour
turning left from LWB westbound into the office trailer/laydown area site in the AM peak hour. The
opposing 668 Thru and Right Turn vehicles may not provide enough gaps to accommodate the left turns.
The EB approach would average 11 vehicles per minute or a vehicle every 6 seconds, which would not
be enough time for the average driver to turn left safely. The Synchro analysis is not sufficient to provide
a true picture of the traffic operation for this situation. It would be better to do a “gap” analysis
following the approved ITE Manual of Transportation Engineering Studies – Gap Study procedure.
Response1: With the Stay at home restrictions and closure due to the COVID-19, the current area
volumes will not reflect the normal conditions.
For the development of this TIA we projected the traffic volumes from 2016 to 2020 using the
methodology and rate provided in the WSDOT’s 44th Street Interchange ICE report. To provide a
conservative analysis, the 2020 projected volumes included the 2025 turning volumes at the existing
intersection of 44th Street at Seahawks Way and 44th Street at 43rd Street.
The traffic analysis was completed using the methodology provided in the current version of the
Highway Capacity Manual (HCM). At the intersection of 44th Street at Seahawks Way, the eastbound
and westbound approaches are free flowing movements and the NB and SB approaches are stop
controlled. Per HCM 6 and 2010, the acceptable gap for left turns from an uncontrolled approach is 4.1
seconds. hence the acceptable gap for westbound left-turn is 4.1 seconds. Taking into consideration the
heavy vehicles making a left turn to enter this facility, per the HCM 6 methodology, this acceptable gap
is adjusted to 4.12 seconds.
In the AM peak eastbound through and right turning traffic totals 675+13 =688 vehicles in the peak
hour. This results in approximately 12 cars per minute with a gap of at least 5 seconds per car, which
results in a gap greater than the acceptable gap of 4.12 seconds for the left-turn.
The westbound through and right traffic totals 200 vehicles in the peak hour and is considerably smaller
than the eastbound through/right traffic. This equates to approximately 3 vehicles per minute and
approximately 20 seconds per vehicles. Hence the HCM results in no queue for the westbound
approach. Sim-Traffic Simulation model also shows no queuing at this westbound approach.
In the PM peak hour, the westbound traffic/right increases to 595 vehicles in the peak hour, while the
westbound left-turn is only about 11 vehicles per hour, which is only about two percent of the total
westbound traffic. Also the eastbound through traffic is approximately 222 vehicles in the peak hour,
Response to Comments: Flatiron-Lane JV TIA
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equating to approximately 4 vehicles per minutes and assuming uniform flow, a gap of 15 seconds is
anticipated between vehicles, which is adequate for the left turning vehicles to make the turn, without
resulting in a queue.
The intersection analysis considers the traffic movements into and out of Seahawks Way. The delay
experiences at Seahawks Way is in the range of 26 – 33.2 seconds per vehicle and LOS D, which in the
acceptable range of delay at a stop-controlled approach of a two-way stop controlled intersection.
Comment 2: If there is a significant delay for the left turns without a left turn lane, it will cause a backup
in the one WB lane on LWB that could back up to the interchange ramp intersection since the two
intersections are so close to each other. That is why there’s a left turn lane EB on LWB at Seahawks Way
to not create a backup in the one thru lane. The additional analysis should look at providing a left turn
lane at this intersection.
From the Sim-Traffic simulation, queuing was not observed at this location. However, if a left-turn lane
is provided, the raised median can be removed to provide a minimum 10-foot-wide turn lane.
Upon your review of this information, please feel free to contact me with your question or comments or
need additional information.
Regards,
Wood Environment & Infrastructure Solutions, Inc.
Anita Johari, PE, PTOE, ENV SP
Lead Traffic Engineer