The Traffic Calming Program (TCP) undertook a streamlined speed bump project in the Summer of 1997 to address traffic problems identified by residents along SE Crystal Springs from 72nd to 82nd Avenue.
The goal of the project was to enhance street safety and livability by reducing the 85th percentile speed of vehicles using SE Crystal Springs closer to the legal maximum speed limit of 25 miles per hour (mph). Speed bumps are the only devices considered for streets like SE Crystal Springs, 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 affecting access. It is not an intended goal to reduce traffic volume on low-volume Local Service Streets.
SE Crystal Springs serves a single family residence neighborhood. 72nd Avenue, to the east, is a Neighborhood Collector street. 82nd Avenue, at SE Crystal Springs's west end, is a Major City Traffic street. SE Crystal Springs has neither side walks nor curbs.
Residents along SE Crystal Springs were invited to an open house October 22, 1997 to review and comment on the proposed speed bump installation. Twelve people attended the open house. Most of those who attended expressed approval for the proposed project. There was concern expressed about an increase in noise and collisions due to the bumps. A petition was available at the open house for residents along SE Crystal Springs to sign and was circulated after the open house by a local resident. Petition results were as follows:
|Category||Number||Percent of Total|
Six 14-foot speed bumps, at 340 to 400 foot spacing, were constructed along the 0.49 mile length of SE Crystal Springs, 72nd to 82nd Avenue, on April 4, 1998 by the Bureau of Maintenance.
As the graph (over) shows, vehicle speeds, previously spread between 26 and 37 mph, have been concentrated into the range of 20 to 25 mph. The average 85th percentile vehicle speed before the project was 36 mph. Since bump construction the average 85th percentile speed is 25 mph and ranges from a low of 19 mph (near the bumps) to a high of 28 mph in the 25 mph zone. Before installation of the speed bumps 78% of drivers exceeded the posted speed limit of 25 mph and 22% exceeded the limit by 10 mph or more. Since bump construction 12% of drivers exceed the posted speed limit and 0.5% exceed the limit by 10 mph or more.
Traffic volumes measured before bump construction averaged 1080 vehicles per day (vpd) and varied from 980 to 1170 vpd. After bump construction volumes averaged 750 vpd and varied from 630 to 880 vpd. Traffic volumes measured on side streets parallel to SE Crystal Springs showed no significant increases from volumes measured before speed bump construction.
Traffic Calming on SE Crystal Springs, 72nd to 82nd Avenue has successfully reduced the average 85th percentile speed closer to the posted speed, enhancing street safety and livability.