The Traffic Calming Program (TCP) undertook a speed bump project in the Spring of 1994 to address traffic problems identified on SW Sunset Boulevard between Capitol Highway and Dosch Road as part of the Westside Corridor Traffic Management Plan.
The goal of the project was to mitigate high speeds from expected use of Sunset Boulevard as an alternative to principal routes due to congestion caused by light rail construction on Highway 26. Speed bumps also enhance street safety and livability by reducing the 85th percentile speed of vehicles using SW Sunset closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps have proven to be effective tools to reduce vehicle speed without impacting access, though volume reductions are typical.
SW Sunset Boulevard, a Neighborhood Collector, provides access to several single family residence neighborhoods in a rural urban setting. Capitol Highway, to the southeast, is a Major City Traffic Street and Dosch Road, to the northwest, is a Neighborhood Collector. SW Sunset has neither curbs or sidewalks and is a designated transit and primary fire response route. SW Sunset Boulevard between Capitol Hwy and Dosch has several horizontal curves limiting sight distance. A significant portion of the daily traffic on SW Sunset Boulevard is believed to be cut-through traffic.
A petition for residents along SW Sunset Boulevard to sign was circulated by a local resident. Of the 106 households along the street, 69, or 65%, signed the petition requesting speed bump installation.
Nine 22-foot speed bumps, at 450 to 830 foot spacing, were constructed along the 1.2 mile stretch of SW Sunset in August of 1994 by the Bureau of Maintenance.
As the graph shows, vehicle speeds, previously concentrated between 29 and 37 mph, have been shifted into the range of 26 to 31 mph. The average 85th percentile vehicle speed before the project was 38 mph. After bump construction the average 85th percentile speed was 31 mph and ranged from a low of 28 mph (near the bumps) to a high of 36 mph.
Traffic volumes measured before bump construction were 2400-4700 vehicles per day (vpd). After bump construction volumes measured 1800-4100 vpd. In both cases the vehicle volumes increased toward Capitol Highway.
A summary of reported accidents is presented in Table 1, below
Table 1. Reported Accidents
Barbur to Dosch
|16 Months Before Project||5||3||2||2|
|16 Months After Project||7||6||1||1|
Traffic Calming on SW Sunset has successfully reduced the 85th percentile closer to the posted speed, reduced traffic volumes, and enhanced street livability.