Final Project Evaluation
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 NE Alberta Street from 42nd Avenue to Cully Boulevard. The
goal of the project was to enhance street safety and livability by reducing the
85th percentile speed of vehicles using Alberta Street closer to the legal
maximum speed limit of 25 miles per hour (mph).
Speed bumps are the only devices considered for streets like Alberta
Street, which are classified as Local Service Streets (are not Transit or
primary Emergency Response Streets), 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 Alberta Street is in a single family residence
neighborhood. To the west, 42nd Avenue is a Neighborhood Collector Street.
At Alberta Street's east end, Cully Boulevard is a Neighborhood Collector
Street. There are no sidewalks or curbs on this portion of Alberta Street.
Residents along Alberta Street were invited to an open house held December
8, 1998, to review and comment on the proposed speed bump installation. Most of
the residents who attended the open house expressed approval for the proposed
project. A petition was available at the open house for residents along Alberta
Street to sign, and was circulated after the open house by a local resident.
Petition results were as follows:
Percent of Total
On March 31, 1999, the Bureau of Maintenance constructed eight 14-foot
speed bumps, at 450- to 500-foot spacing, along the 0.73-mile length of Alberta
Street from 42nd Avenue to Cully Boulevard.
As the graph shows, vehicle speeds that previously peaked between 29 to 31
mph now peak between 23 to 25 mph. The average 85th percentile speed before the
project was 36 mph. Since bump construction, the average 85th percentile speed
is 25 mph. Before installation of the speed bumps, 80 percent of drivers
exceeded the posted 25-mph speed limit, and 20 percent exceeded the limit by 10
mph or more. Since bump construction, 34 percent of drivers exceed the posted
speed limit and 2.4 percent exceed the limit by 10 mph or more.
Traffic volumes measured before bump construction averaged 1,183 vehicles
per day (vpd). After the speed bumps were installed, volumes averaged 910
Traffic calming on NE Alberta Street from 42nd Avenue to Cully Boulevard
has successfully reduced the average 85th percentile speed closer to the posted
speed, enhancing street safety and livability.