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Portland Bureau of Transportation

Phone: 503-823-5185

Fax: 503-823-7576

1120 SW Fifth Ave, Suite 800, Portland, OR 97204

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SW Slavin - Seymour to south end

Final Project Evaluation


The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Summer of 1997 to address traffic problems identified by residents along SW Slavin Road, south of Seymour Street.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SW Slavin Road closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only devices considered for streets like SW Slavin Road, which are classified as Local Service Streets, are not transit or primary fire response routes and have vehicle volumes between 400 and 1700 vehicles per day. Speed bumps have proven to be effective tools to reduce vehicle speed without affecting access. It is not an intended goal to reduce traffic volume on low-volume Local Service Streets.
SW Slavin Road serves a primarily multi family residence neighborhood. Seymour Street, at SW Slavin Road's north end, is a Local Service street. SW Slavin dead ends at its south end. SW Slavin Road has only occasional side walks and curb and there are horizontal and vertical curves which limit sight distances.

Open House

Residents along SW Slavin Road were invited to an open house October 15, 1997 to review and comment on the proposed speed bump installation. Five people attended the open house. All those who attended expressed approval for the proposed project. A petition was available at the open house for residents along SW Slavin Road to sign and was circulated after the open house by local residents. The results of the signature gathering are summarized below:
Category Number Percent of Total
No Signature 33 14.2%
Don't Care 4 1.7%
Not in Favor 28 12.1%
In Favor 166 71.9%
Vacant 11  
In Favor but Not on Slavin


Six 14-foot speed bumps, at 300 to 900 foot spacing, were constructed along the 0.64 mile length of SW Slavin Road, south of Seymour, on April 4, 1998 by the Bureau of Maintenance.

Vehicle Speeds

As the graph (over) shows, vehicle speeds, previously spread between 26 and 34 mph, have been concentrated into the range of 20 to 25 mph. The average 85th percentile vehicle speed before the project was 31 mph. Since bump construction the average 85th percentile speed is 24.6 mph and ranges from a low of 18 mph to a high of 29 mph. Before installation of the speed bumps 64% of drivers exceeded the posted speed limit of 25 mph and 5% exceeded the limit by 10 mph or more. Since bump construction 17% of drivers exceed the posted speed limit and 0.4% exceed the limit by 10 mph or more.

Traffic Volume

Traffic volumes measured before bump construction averaged 750 vehicles per day (vpd) and varied from 130 vpd, near the top, to 1200 vpd, at the bottom. Traffic volume measures since bump construction show no variation. Since Slavin Road is a dead-end street, no adjacent parallel diversion routes were identified.


Traffic Calming on SW Slavin Road, south of Seymour, has successfully reduced the average 85th percentile speed closer to the posted speed, enhancing street safety and livability.