The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Summer of 1996 to address traffic problems identified by residents along NE 110th Avenue from 111th to Glisan.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using NE 110th Avenue closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like NE 110th 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.
NE 110th Avenue serves a single family residence neighborhood. NE 111th Avenue, to the north, is a Local Service street. Glisan, at NE 110th Avenue's south end, is a Major City Traffic street. NE 110th Avenue has partial sidewalks and curbs at the north end. A large portion of the daily traffic on NE 110th Avenue is believed to be cut-through traffic due to a traffic signal at Halsey Street and another speed bump project on NE 111th Avenue.
All residents along NE 110th Avenue were invited to an open house June 12, 1996 to review and comment on the proposed speed bump installation. 21 households were represented at the open house. The majority of those who attended expressed approval for the proposed project. A petition was available at the open house for residents along NE 110th Avenue to sign and was circulated after the open house by a local resident. Of the 54 households along the street, 43, or 79.6%, signed the petition requesting speed bump installation.
Four 14-foot speed bumps, at 520 to 580 foot spacing, were constructed along the 0.44 mile stretch of NE 110th Avenue, 111th to Glisan, on September 28, 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. Since bump construction the average 85th percentile speed is 24.2 mph and ranges from a low of 21 mph (near the bumps) to a high of 28 mph.
Traffic volumes measured before bump construction averaged 640 vehicles per day (vpd) and varied from 500 to 700, with higher volumes near the street ends. After bump construction volumes averaged 480 vpd and varied from 420 to 570 vpd. Traffic volumes measured on side streets adjacent to NE 110th Avenue showed no significant increases from volumes measured prior to speed bump construction.
Traffic Calming on NE 110th Avenue, 111th to Glisan has successfully reduced the 85th percentile closer to the posted speed, enhancing street safety and livability.