The Traffic Calming Program (TCP) undertook a Streamlined Speed Bump Project in the Fall of 1995 to address traffic problems identified by residents along SE Morrison from 117th to 122nd Avenue.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE Morrison closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like SE Morrison, 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 Morrison serves a mixed single family residence and apartment neighborhood. Southeast 117th, to the west, is a Neighborhood Collector street. Southeast 122nd, at SE Morrison's east end, is a Major City Traffic street. SE Morrison has neither sidewalks or curbs for most of its length. A large portion of the daily traffic on SE Morrison is believed to be cut-through traffic due to commercial uses at the street's east end and congestion on SE 122nd.
All residents along SE Morrison were invited to an open house November 8, 1995 to review and comment on the proposed speed bump installation. Four households were represented at the open house. Those who attended expressed approval for the proposed project. A petition was available at the open house for residents along SE Morrison to sign and was circulated after the open house by a local resident.
Three 14-foot speed bumps, at approximately 400 foot spacing, were constructed along the 0.24 mile stretch of SE Morrison, 117th to 122nd Avenue, in April of 1996 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 85th percentile vehicle speed before the project was 34.6 mph. After bump construction the average 85th percentile speed is 22.1 mph and ranges from a low of 20 mph (near the bumps) to a high of 27 mph.
Traffic volumes measured before bump construction were 990 vehicles per day (vpd). After bump construction volumes measured 800-960 vpd. Traffic volumes measured on side streets adjacent to SE Morrison showed no significant increases from counts taken before speed bump construction.
Traffic Calming on SE Morrison, 117th to 122nd Avenue has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.