The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Summer of 1997 to address traffic problems identified by residents along SE Martins from 28th to 32nd Avenue.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE Martins closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only devices considered for streets like SE Martins, 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 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.
SE Martins serves a single family residence neighborhood. SE 28th Avenue, to the west, is a Neighborhood Collector street. SE 32nd Avenue, at SE Martins's east end, is a Local Service street. SE Martins has side walks and curbs. Additionally, there are horizontal curves and a slight grade toward 28th Avenue. A large portion of the daily traffic on SE Martins is believed to be cut-through traffic avoiding the intersection of 28th and Woodstock. This movement is facilitated by an all-way stop at 32nd and Woodstock, a Neighborhood Collector adjacent to Reed College.
Residents along SE Martins were invited to an open house October 2, 1997 to review and comment on the proposed speed bump installation. Sixteen people attended the open house. Most of those who attended expressed approval for the proposed project. There was concern expressed about the appearance of the bumps as well as fears the bumps would cause a large change in traffic patterns on adjacent streets. A petition was available at the open house for residents along SE Martins to sign and was circulated after the open house by a local resident. Petition results were as follows:
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Two 14-foot speed bumps, at 417 foot spacing, were constructed along the 0.14 mile length of SE Martins, 28th to 32nd Avenue, on April 5th and 17th, 1998 by the Bureau of Maintenance. One of the bumps was a test installation of a rubber speed bump.
As the graph (over) shows, vehicle speeds, previously spread between 23 and 31 mph, have been shifted into the range of 20 to 22 mph. The average 85th percentile vehicle speed before the project was 32 mph. Since bump construction the average 85th percentile speed is 24.6 mph and ranges from a low of 18 mph (near the bumps) to a high of 28 mph in the 25 mph zone. Before installation of the speed bumps 53% of drivers exceeded the posted speed limit of 25 mph and 6% exceeded the limit by 10 mph or more. Since bump construction 13% of drivers exceed the posted speed limit and 0.3% exceed the limit by 10 mph or more.
Traffic volumes measured before bump construction averaged 448 vehicles per day (vpd). After bump construction volumes averaged 347 vpd. Traffic volumes measured on side streets parallel to SE Martins showed no significant increases from volumes measured before speed bump construction.
Traffic Calming on SE Martins, 28th to 32nd Avenue has successfully reduced the average 85th percentile speed closer to the posted speed, enhancing street safety and livability.