Final Project Evaluation
The Bureau of Transportation System Management undertook a Residential
Speed Bump Purchase (RSBP) Project in the spring of 1999 to address traffic
problems identified by residents along NW Thurman Street between 27th and
Aspen Avenues. The goal of the project was to enhance street safety and
livability by reducing the 85th percentile speed of vehicles using Thurman
Street closer to the legal maximum speed limit of 25 miles per hour (mph).
This segment of Thurman Street is classified as a Neighborhood Collector,
with volumes between 1,000 and 4,000 vehicles per day (vpd). It is also a
Transit Street. Speed bumps have proven to be effective tools for reducing
vehicle speed without affecting access.
This section of Thurman Street is in a mixed neighborhood of single family
residences, apartments, and retail stores. There are curbs and sidewalks along
this segment, but not in the segment of Thurman Street from Aspen Avenue to
the park, where it ends. The closest Collectors are 23rd Avenue to the east
and Vaughn Street to the north.
Thurman Street west of 27th Avenue is classified as a Neighborhood
Collector Street. Prior to the Thurman Street RSBP Project, policies provided
for projects only on streets classified as Local Service. City Council approved
a change in policy to provide for RSBP Projects on Neighborhood Collector
Streets in the summer of 1999.
Residents along Thurman Street were invited to an open house on April 14,
1999, to review and comment on the proposed speed bump installation. Most of the
22 people who attended expressed approval for the proposed project. A petition
was available at the open house for residents along Thurman Street to sign and
was circulated after the open house by a local resident. Petition results were
Percent of Total
On August 12, 1999, the Bureau of Maintenance constructed eight 22-foot
speed bumps along the 0.9-mile length of Thurman Street between 27th and Aspen
Avenues. Intervals between bumps varied due to the unique gradient, geometry,
and character of Thurman Street, which includes a bridge, steep slopes, and many
As the graph shows, vehicle speeds that previously peaked between 29 and 31
mph, now peak between 23 and 25 mph. The average 85th percentile vehicle speed
before the project was 34.5 mph. Since bump construction, the average 85th
percentile speed dropped to 28 mph. Before the installation of speed bumps, 83%
of drivers exceeded the posted speed limit of 25 mph and 14% exceeded the limit
by 10 mph or more. Since bump construction 33% of drivers exceed the posted
speed limit and 2% exceed the limit by 10 mph or more.
Traffic volumes measured before bump construction averaged 3,119 vehicles
per day (vpd). After bump construction, volumes averaged 2,852 vpd.
Traffic calming on NW Thurman Street between 27th and Aspen Avenues has
successfully reduced the average 85th percentile speed closer to the posted
speed. No comparative study of traffic diversion has been done. This is because
there is no street for any significant diversion in this project area. Thurman
Street is the main neighborhood exit. This is confirmed by the approximate
equality in Thurman Street volumes before and after the project.