The Traffic Calming Program (TCP) undertook a project in the Winter of 1995 to address traffic problems identified by residents along NE 57th Avenue between NE Halsey Street and NE Hassalo Street.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using NE 57th closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like NE 57th, 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 57th serves a mixed single family residence, apartment and industrial neighborhood. NE Halsey Street, to the North, is a Neighborhood Collector Street. NE Hassalo Street, at NE 57th's South end, is a Local Service Street. NE 57th is fronted on one side by Normandale Park. A significant percent of the daily traffic on NE 57th is believed to be cut-through traffic. There is a traffic signal at Halsey which may contribute to this. Additionally the park has a ball field and is heavily used during spring and summer.
All residents along NE 57th Avenue were invited to an open house February 28, 1995 to review and comment on the proposed speed bump installation. Seven households were represented at the open house. The majority of those who attended expressed approval for the proposed project. There was concern expressed about the noise generated by the bumps. A petition was available at the open house for residents along NE 57th to sign and was circulated after the open house by a local resident. Of the 23 households along the street, 17, or 73.9%, signed the petition requesting speed bump installation.
Three 14-foot speed bumps, at approximately 500 foot spacing, were constructed along the 0.24 mile stretch of NE 57th in June of 1995 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 28 mph. The 85th percentile vehicle speed before the project was 30 mph. After bump construction the average 85th percentile speed was 24.4 mph and ranged from a low of 18 mph (near the bumps) to a high of 28 mph.
Traffic volumes measured before bump construction ranged from 1100-1500 vehicles per day (vpd). After bump construction volumes measured 800-1000 vpd. Adjacent streets that were identified as unwanted diversion routes showed no significant increases in traffic volume.
Traffic Calming on NE 57th Avenue has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.