The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Fall of 1996 to address traffic problems identified by residents along N/NE Dekum from Vancouver to M. L. King Jr. Boulevard.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using N/NE Dekum closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only device considered for streets like N/NE Dekum, 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/NE Dekum serves a single family residence neighborhood with apartments and commercial uses at its east end. Vancouver Avenue, to the west, is a Neighborhood Collector street. M. L. King Jr. Boulevard, at NE Dekum's east end, is a Major City Traffic street with a signal. N/NE Dekum is generally a straight, flat street and has sidewalks and curbs its entire length on both sides. There is a school zone at the west end for two blocks adjacent to Holy Redeemer school. Part of the daily traffic on N/NE Dekum is believed to be cut-through traffic due to the traffic signal at M. L. King Jr. Boulevard.
Residents along N/NE Dekum were invited to an open house October 22, 1996 to review and comment on the proposed speed bump installation. No households were represented at the open house. A petition was available at the open house for residents along N/NE Dekum to sign and was circulated after the open house by a local resident. Of the 34 households along the street, 24, or 70.6%, signed the petition requesting speed bump installation.
Five 14-foot speed bumps, at 260 to 460 foot spacing, were constructed along the 0.35 mile stretch of N/NE Dekum, Vancouver to M. L. King Jr. Boulevard, April 12, 1997 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 20 to 28 mph. The average 85th percentile vehicle speed before the project was 35.5 mph. After bump construction the average 85th percentile speed is 27 mph and ranges from a low of 21 mph (near the bumps) to a high of 29 mph.
Traffic volumes measured before bump construction were 1500 vehicles per day (vpd). After bump construction volumes average 880 vpd with the highest volume, 1000 vpd, measured at the east end. This represents a 33% reduction in vehicle volume compared to measurements prior to speed bump construction. Traffic volumes measured on the next two side streets north of N/NE Dekum also showed a decrease in volume.
Traffic calming on N/NE Dekum, Vancouver to M. L. King Jr. Boulevard, has successfully reduced the 85th percentile closer to the posted speed and enhanced street safety and livability.