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 111th Avenue from Division to Powell.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE 111th 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 111th 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 111th Avenue serves a mixed single family residence and apartment neighborhood. Division Street, to the north, is a Major City Traffic street. Powell Boulevard, at SE 111th Avenue's south end, is a Neighborhood Collector street. SE 111th Avenue has partial sidewalks and curbs. A portion of the daily traffic on SE 111th Avenue is believed to be cut-through traffic due to localized congestion.
All residents along SE 111th Avenue were invited to an open house June 11, 1996 to review and comment on the proposed speed bump installation. Seventeen people attended the open house. The majority of those who attended expressed approval for the proposed project. Some in attendance considered the bumps to be excessive. A petition was available at the open house for residents along SE 111th Avenue to sign and was circulated after the open house by a local resident. Of the 109 households along the street, 88, or 80.7%, signed the petition requesting speed bump installation.
Six 14-foot speed bumps, at 380 to 680 foot spacing, were constructed along the 0.53 mile stretch of SE 111th Avenue, Division to Powell, on September 27, 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 average 85th percentile vehicle speed before the project was 31.9 mph. After bump construction the average 85th percentile speed is 24 mph and ranges from a low of 15 mph (near the bumps) to a high of 30 mph.
The traffic volume measured before bump construction averaged 600 vehicles per day (vpd), and ranged from 490-740 vpd. After bump construction volumes averaged 470 vehicles per day (vpd), and ranged from 330-710 vpd. Traffic volumes measured on side streets adjacent to SE 111th Avenue showed no significant increases from volumes measured prior to speed bump construction.
Traffic Calming on SE 111th Avenue, Division to Powell has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.