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 Streets.

 

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:

 

Category	Number	Percent of Total
Yes	49	67.1%
No	0	-
No Signature	24	32.9%
Total	73	100%

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 11^th and 13^th Avenues decreased after construction. Traffic volumes measured on 12^th 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.