The Traffic Calming Program (TCP) undertook a Streamlined Speed Bump Project in the Fall of 1995 to address traffic problems identified by residents along N Missouri from Killingsworth to Holman.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using N Missouri closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like N Missouri, 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.
N Missouri serves a single family residence neighborhood. Killingsworth, to the south, is a Neighborhood Collector street. Holman, at N Missouri's north end, is a Local Service street. N Missouri has sidewalks and curbs. A large portion of the daily traffic on N Missouri is believed to be cut-through traffic due to a freeway off ramp south of Killingsworth.
All residents along N Missouri were invited to an open house October 24, 1995 to review and comment on the proposed speed bump installation. One household was represented at the open house. Those who attended expressed approval for the proposed project. A petition was available at the open house for residents along N Missouri to sign and was circulated after the open house by a local resident. Of the 30 households along the street, 25, or 83.3%, signed the petition requesting speed bump installation.
Five 14-foot speed bumps, at 400 to 500 foot spacing, were constructed along the 0.38 mile stretch of N Missouri, Killingsworth to Holman, in June of 1996 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 23 to 28 mph. The average 85th percentile vehicle speed before the project was 35.5 mph. Since bump construction the average 85th percentile speed is 25.5 mph and ranges from a low of 19 mph (near the bumps) to a high of 28 mph.
Traffic volumes measured before bump construction were 640-700 vehicles per day (vpd) south of Ainsworth and 140 vpd north of Ainsworth. After bump construction volumes measured 640-720 vpd to the south and 90 vpd to the north. Traffic volumes measured on side streets adjacent to N Missouri showed variable changes from volumes measured prior to speed bump construction, though none exceeded minimum thresholds which require mitigation.
Traffic Calming on N Missouri, Killingsworth to Holman has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.