The Traffic Calming Program (TCP) undertook a Streamlined Speed Bump Project in the Winter of 1994 on NE 113th Avenue between Glisan Street and Burnside Avenue.
The goal of the project was to enhance street safety by reducing the 85th percentile speed of vehicles using NE 113th closer to the posted speed limit. Speed bumps are the only device considered for streets like NE 113th, 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 113th Avenue serves a single-family residence neighborhood. The South intersection at Burnside has a traffic signal and provides access across the MAX light-rail tracks. The North intersection at Glisan is stop-controlled on 113th only. A significant percent of the daily traffic on NE 113th Avenue is believed to be cut-through traffic due to the signal at Burnside.
All residents along NE 113th were invited to an open house February 16, 1995 in order to review and comment on the proposed bump installation. Five 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 the street to sign and was circulated after the open house by a local resident. Of the 19 households along NE 113th, 16, or 84%, signed the petition requesting speed bump installation.
Three 14-foot speed bumps were constructed in March of 1995 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 17 to 25 mph. The 85th percentile vehicle speed before the project was 35 mph. After bump construction the 85th percentile speed averaged 26 mph and ranged from a low of 21 mph (near a bump) to a high of 30 mph.
Traffic Volumes measured after bump construction showed no significant change from the pre-bump volumes of 1100-1300 vehicles per day (vpd). Adjacent streets that were identified as unwanted diversion routes showed no significant increases in traffic volume.
Traffic Calming on NE 113th has successfully reduced overall speed and enhanced street safety.