The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Fall of 1996 to address traffic problems identified by residents along NE 47th Avenue from Prescott to Fremont.
The goal of the project was to enhance street safety by reducing the 85th percentile speed of vehicles using NE 47th Avenue closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only devices considered for streets like NE 47th Avenue, which are classified as Local Service Streets, are not transit or primary fire response routes and have vehicle volumes between 400 and 1700 vehicles per day. Speed bumps are 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 47th Avenue serves a single family residence neighborhood. Prescott, to the north, and Fremont, at NE 47th Avenue's south end, are Neighborhood Collector streets. NE 47th Avenue has sidewalks and curbs except a portion just south of its midpoint. Part of the daily traffic on NE 47th Avenue is believed to be cut-through traffic due to congestion on the next parallel collector, NE 42nd, to the west.
Residents along NE 47th Avenue were invited to an open house September 4, 1996 to review and comment on the proposed speed bump installation. Eleven households were represented at the open house. The majority of those who attended expressed approval for the proposed project. There was concern expressed regarding emergency response. A petition was available at the open house for residents along NE 47th Avenue to sign and was circulated after the open house by a local resident. Of the 48 households along the street, 32, or 67%, signed the petition requesting speed bump installation.
Six 14-foot speed bumps, at 380 to 480 foot spacing, were constructed along the 0.49 mile stretch of NE 47th Avenue, Prescott to Fremont, on April 18, 1997 by the Bureau of Maintenance.
As the graph shows, vehicle speeds, previously concentrated between 26 and 31 mph, have been shifted into the range of 20 to 25 mph. The average 85th percentile vehicle speed before the project was 34.6 mph. After bump construction the average 85th percentile speed is 25.4 mph and ranges from a low of 21 mph (near the bumps) to a high of 27 mph. Before installation of the speed bumps 67% of drivers exceeded the posted speed limit of 25 mph and 10% exceeded the limit by 10 mph or more. Since bump construction 15.7% of drivers exceed the posted speed limit and 0.4% exceed the limit by 10 mph or more.
Traffic volume before bump construction ranged from 940-1280 vehicles per day (vpd). After bump construction volumes range from 1050-1680 vehicles per day and average 1300 vpd.
Traffic Calming on NE 47th Avenue, Prescott to Fremont, has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.