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2813 Rockefeller Avenue Suite B Everett, WA 98201
Tel: 425-339-8266 Fax: 425-258-2922 E-mail: info@gibsontraffic.com
Queuing Analysis Memorandum
To: Nick Wecker, Senior Planner
Barghausen Consulting Engineers, Inc.
From: Brad Lincoln, PE
Subject: Queuing Analysis
Project: Renton Brown Bear Car Wash
GTC #21-372
Date: January 31, 2022
Gibson Traffic Consultants, Inc. (GTC) has been requested to provide a queuing analysis for the
Brown Bear Car Wash located at 800 Grady Way in the City of Renton. There is an existing tunnel
car wash currently on the site, which also includes a gas station with convenience store and a self-
serve car wash area. The current tunnel car wash has a single queue lane and capacity for 5 to 6
vehicles. There are currently traffic control devices on the site to help with the flow of vehicles into
the tunnel car wash. It is therefore assumed that vehicles routinely queue beyond the marked crossing
area and into the drive aisle.
The proposal is to construct an Auto Sentry with two payment kiosks for the existing tunnel car wash
to provide unattended, point-of-sale transactions. The proposal will not affect the operations of the
tunnel car wash with regards to service capacity. However, there is a request for a reduced minimum
setback for the Auto Sentry, which triggers the need for this analysis.
1. TRIP GENERATION
The trip generation calculations for the existing Brown Bear Car Wash development have been
performed using trip generation data contained in the Institute of Transportation Engineers’ (ITE)
Trip Generation Manual, 11th Edition (2021). The average trip generation rates for ITE land Use
Code (LUC) 948, Automated Car Wash, has been used to determine the weekday PM peak-hour trip
generation of the existing car wash. ITE data shows a trip generation rate of 77.5 trips, 50% inbound
and 50% outbound, per tunnel. This means the existing Brown Bear Car Wash generates
approximately 80 weekday PM peak-hour trips. This equates to 40 vehicles per hour using the car
wash. The trip generation data is included in the attachments.
Brown Bear Car Wash Queuing Analysis
Gibson Traffic Consultants, Inc. January 2022
info@gibsontraffic.com 2 GTC #21-372
2. ON-SITE QUEUING
The existing Brown Bear Car Wash can service two vehicles at a time and is proposed to include
space for a total of 8 vehicles between the drive aisle/marked crossing area and the car wash tunnel.
This includes two vehicles at each of the payment kiosks (4 total vehicles) and 4 vehicles between
the payment kiosks and the tunnel. The tunnel is able to serve 55 vehicles per hour based. The number
of vehicles that are anticipated to be queued has been calculated using the service rate and anticipated
arrival rate of 40 vehicles in an hour (based on the gross PM peak-hour trip generation of 78 vehicles).
The calculations show that the 8 vehicles queued outside the tunnel equates to the 94th Percentile
queue.
It is important to note that the queue calculations account for only 1 vehicle in the tunnel at a time.
Including a second vehicle would result in a theoretical queue of 9 vehicles. This equates to a 96th
Percentile queue. This means that the additional payment kiosk and queuing area will provide for
approximately the 95th Percentile queue length, meaning there is a 95% probability that the queue
length will be within the provided area. The queues should therefore not significantly impact the
operations of the site.
3. CONCLUSIONS
The proposed Auto Sentry payment kiosks will increase the queuing area by approximately 60% (5
vehicles to 8 vehicles) and it anticipated to decrease the likelihood of vehicles impacting the drive
aisle and marked crossing area. The Auto Sentry payment kiosks are anticipated to improve the
operations of the site.
A
Attachments