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Portland Bureau of Transportation

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Phone: 503-823-5185

Fax: 503-823-7576

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SE 128th Avenue- Foster to Holgate

Final Project Evaluation

Introduction

The Bureau of Transportation System Management undertook a Streamlined Speed Bump Project in the fall of 1998 to address traffic problems identified by residents along SE 128th Avenue from Foster Road to Holgate Boulevard. The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using 128th Avenue closer to the legal maximum speed limit of 25 miles per hour (mph).
 
Speed bumps are the only devices considered for streets like 128th Avenue, which are classified as Local Service Streets (are not Transit or primary Emergency Response Routes) and have vehicle volumes between 400 and 2,000 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.
 
This section of 128th Avenue is in a single family residence neighborhood. To the south, Foster Road is a District Collector street. At 128th Avenue's north end, Holgate Boulevard is a Neighborhood Collector Street. There are no sidewalks or curbs on this portion of 128th Avenue.

Open House

Residents along 128th Avenue were invited to an open house on October 27, 1998, to review and comment on the proposed speed bump installation. Most of the 42 people who attended expressed approval for the proposed project. A petition was available at the open house for residents along 128th Avenue to sign, and was circulated after the open house by a local resident. Petition results were as follows:
 
 
Vote
Amount
Percent of Total
Yes
116
77.33%
No
11
7.33%
No Signature
23
15.34%
Totals
150
100%

Performance

On June 13, 1999, the Bureau of Maintenance constructed eight 14-foot speed bumps, at 400- to 450-foot spacing, along the 0.79-mile length of 128th Avenue from Foster Road to Holgate Boulevard.

Vehicle Speeds

As the graph shows, vehicle speeds that previously peaked between 29 to 31 mph, now range between 20 to 22 mph. The average 85th percentile vehicle speed before the project was 36 mph. Since bump construction, the average 85th percentile speed is 26 mph and ranges from a low of 24 mph (near the bumps) to a high of 30 mph in the 25-mph zone. Before installation of the speed bumps, 83.7 percent of drivers exceeded the posted 25-mph speed limit, and 20.9 percent exceeded the limit by 10 mph or more. Since bump construction 31.5 percent of drivers exceed the posted speed limit and
 
 
2.1 percent exceed the limit by 10 mph or more.

Traffic Volume

Traffic volumes measured before bump construction averaged 1,490 vehicles per day (vpd). After the speed bumps were installed, volumes averaged 1,500 vpd and varied from 1,200 to 1,550 vpd.

Conclusion

Traffic calming on SE 128th Avenue from Foster Road to Holgate Boulevard has successfully reduced the average 85th percentile speed closer to the posted speed, enhancing street safety and livability.
 

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