Final Project Evaluation
The Traffic Calming Program (TCP) undertook a speed bump purchase project
in the fall of 1998 to address traffic problems identified by residents along NE
14th Avenue from Fremont to Knott.
The goal of the project was to enhance street safety and livability by
reducing the 85th percentile speed of vehicles using NE 14th Avenue closer to
the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the
primary device considered for streets like NE 14th Avenue, which are classified
as Local Service Streets, are not transit or primary fire response routes and
have vehicle volumes between 400 and 2000 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
NE 14th Avenue serves a single family residence neighborhood. Fremont, to
the north, is a Neighborhood Collector street. Knott, at the project's south
end, is a Local Service street. NE 14th Avenue has sidewalks and curbs.
Residents along NE 14th Avenue were invited to an open house September 15,
1998 to review and comment on the proposed speed bump installation. Twenty-one
people attended the open house. Most of those who attended expressed approval
for the proposed project. Some considered the bumps to be unnecessary. A
petition was available at the open house for residents along NE 14th Avenue to
sign and was circulated after the open house by local residents. Petition
results were as follows:
Percent of Total
The Bureau of Maintenance constructed four 14-foot speed bumps, at 520 to
560 feet spacing, along the 0.42-mile length of NE 14th Avenue, Fremont to
Knott, on September 28, 1999.
As the graph shows, vehicle speeds that previously peaked at 20 to 25 mph
now range between 17 to 25 mph. The average 85th percentile vehicle speed before
the project was 26.5 mph. Since bump construction the average 85th
percentile speed is 23.7 mph and ranges from a low of 21 mph (near the
bumps) to a high of 29 mph in the 25-mph zone. Before installation of the speed
bumps 21.5% of drivers exceeded the posted speed limit of 25 mph and 0.9%
exceeded the limit by 10 mph or more. Since bump construction 9.2% of drivers
were measured to exceed the posted speed limit and 1.7% exceed the limit by 10
mph or more. The low volume of cars using the street and the greater number of
data collection points after construction are primary influences on the higher
posted+10 speed percentage.
Traffic volumes measured before bump construction averaged 420 vehicles per
day (vpd). After bump construction volumes averaged 340 vpd and varied from 280
to 400 vpd. The 80-vehicle drop in traffic volume translates to an average
decrease of 19%. This is relatively high for this type of project. Traffic
volumes measured on 11th and 13th Avenues decreased after
construction. Traffic volumes measured on 12th Avenue increased after
construction, but not high enough to require mitigation.
Traffic Calming on NE 14th Avenue, Fremont to Knott has successfully
reduced the average 85th percentile speed closer to the posted speed, as well as
reduced traffic volume, enhancing street safety and livability.