The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Spring of 1996 to address traffic problems identified by residents along SE 113th Avenue from Burnside to Stark.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE 113th Avenue closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like SE 113th 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 have proven to be effective tools to reduce vehicle speed without impacting access. It is not an intended goal to reduce traffic volume on low-volume Local Service Streets.
SE 113th Avenue serves a single family residence neighborhood with Ventura Park at the south end. Burnside, to the north, is a Neighborhood Collector street. Stark, at SE 113th Avenue's south end, is a Major City Traffic street. SE 113th Avenue has sidewalks and curbs and there is a hill which limits sight distances about midpoint along the street. A portion of the daily traffic on SE 113th Avenue is believed to be cut-through traffic due to localized congestion on the arterial streets and a traffic signal at Burnside where vehicles can cross the MAX rail line.
All residents along SE 113th Avenue were invited to an open house June 13, 1996 to review and comment on the proposed speed bump installation. Thirteen households were represented at the open house. All those who attended expressed approval for the proposed project. A petition was available at the open house for residents along SE 113th Avenue to sign and was circulated after the open house by a local resident. Of the 19 households along the street, 15, or 78.9%, signed the petition requesting speed bump installation.
Three 14-foot speed bumps, at 411 and 425 foot spacing, were constructed along the 0.23 mile stretch of SE 113th Avenue, Burnside to Stark, August 10, 1996 by the Bureau of Maintenance.
As the graph shows, vehicle speeds, previously concentrated between 26 and 34 mph, have been shifted into the range of 20 to 28 mph. The 85th percentile vehicle speed before the project was 34.8 mph. After bump construction the average 85th percentile speed is 24.5 mph and ranges from a low of 22 mph (near the bumps) to a high of 28 mph.
Traffic volumes measured before bump construction were 1100-1200 vehicles per day (vpd). After bump construction volumes measured 900-1100 vpd. It should be noted that the different time of year for the before and after volume measurements may account for the reduced volume Traffic volumes measured on side streets adjacent to SE 113th Avenue showed no increases from volumes measured prior to speed bump construction.
Traffic Calming on SE 113th Avenue, Burnside to Stark has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.