Final Project Evaluation
The Traffic Calming Program undertook a Streamlined Speed Bump Project in the Winter of 1994 on SW Troy Street between Capitol Highway and Capitol Hill Road.
The goal of the project was to enhance street safety by reducing the 85th percentile speed of vehicles using SW Troy closer to the posted speed limit. Speed bumps are the only device considered for streets like SW Troy, 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.
SW Troy Street serves a mixed single family residence and apartment neighborhood. Capitol Highway, to the West, is a District Collector. Capitol Hill Road, at Troy's East end, is a Neighborhood Collector Street. A significant percent of the daily traffic on SW Troy Street is believed to be cut-through traffic en route to a traffic signal at Capitol Hill Road and Barbur Boulevard.
All residents along SW Troy were invited to an open house January 10, 1995 to review and comment on the proposed bump installation. Eighteen 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 SW Troy to sign and was circulated after the open house by a local resident. Of the 82 households along the street, 63, or 76.8%, signed the petition requesting speed bump installation.
Four 14-foot speed bumps, at 419 to 453 foot spacing, were constructed along the 0.42 mile stretch of SW Troy in March of 1995 by the Bureau of Maintenance.
As the graph shows, vehicle speeds, previously concentrated between 29 and 34 mph, have been shifted into the range of 20 to 25 mph. The 85th percentile vehicle speeds measured before the project ranged from 28 mph to 41 mph. After bump construction the average 85th percentile speed was 25.2 mph and ranged from a low of 22 mph (near the bumps) to a high of 28 mph. After bump construction the 85th percentile speed measured was 28 mph.
Traffic volumes measured before bump construction were 1400-1500 vehicles per day (vpd). After bump construction volumes measured 1000-1100 vpd. Adjacent streets that were identified as unwanted diversion routes showed no significant increases in traffic volume.
Traffic Calming on SW Troy has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety.