The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the summer of 1996 to address traffic problems identified by residents along SE 101st Avenue from Harold to Foster.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE 101st Avenue closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only devices considered for streets like SE 101st 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 affecting access. It is not an intended goal to reduce traffic volume on low-volume Local Service Streets.
SE 101st Avenue serves a primarily single family residence neighborhood. Harold, to the north, is a Neighborhood Collector street. Foster, at SE 101st Avenue's south end, is a Major City Traffic street. SE 101st Avenue has sidewalks and curbs. A portion of the daily traffic on SE 101st Avenue is believed to be cut-through traffic due to a traffic signal at Foster.
Residents along SE 101st Avenue were invited to an open house September 18, 1996 to review and comment on the proposed speed bump installation. One household was 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 101st Avenue to sign and was circulated after the open house by a local resident. Of the 37 households along the street, 32, or 86.5%, signed the petition requesting speed bump installation.
Four 14-foot speed bumps, at 450 to 550 foot spacing, were constructed along the 0.36 mile stretch of SE 101st Avenue, Harold to Foster, on May 10, 1997 by the Bureau of Maintenance.
As the graph shows, vehicle speeds, previously concentrated between 23 and 31 mph, have been shifted into the range of 16 to 22 mph. The average 85th percentile vehicle speed before the project was 30 mph. After bump construction the average 85th percentile speed is 23 mph and ranges from a low of 19 mph (near the bumps) to a high of 24 mph.
Traffic volumes measured before bump construction averaged 660 vehicles per day (vpd). After bump construction volumes averaged 550 vpd. Traffic volumes measured on side streets parallel to SE 101st Avenue showed no significant increases from volumes measured before speed bump construction.
Traffic Calming on SE 101st Avenue, Harold to Foster has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.