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SE Clinton, 12th to 21st Avenue

CLINTON BIKEWAY
12th AVENUE TO 21th ANVENUE
Final Project Evaluation
 
Introduction
 
Portland’s Bike Program enlisted the help of the Traffic Calming section for a speed bump project in the spring of 1998. Speed bumps were identified by local citizens as the most appropriate tool to address traffic problems along the project segment of SE Clinton, 12th to 21st Avenues.
 
The goal of the project was to enhance street safety for bicycle riders by reducing the 85th percentile speed of vehicles using SE Clinton closer to the legal maximum speed limit of 25 miles per hour (mph). 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 Clinton, from 12th to 21st Avenues, serves a mixed single family residence and commercial neighborhood. SE 12th Avenue, to the west, is a Major City Traffic street under Portland’s traffic street classification system. SE 21st Avenue, at this project segment's east end, is a Local Service street. Clinton was broken at 21st as a project segment due to Tri-Met bus service between 21st and 26th Avenue. SE Clinton, from 12th to 21st Avenue, is fairly level, is straight, except for a slight jog at 19th, and has parking, sidewalk and curb on both sides.
 
Open House
 
Residents along SE Clinton were invited to an open house June 3, 1998 to review and comment on the proposed speed bump installation. Fourty-five people attended the open house. Most of those who attended expressed approval for the proposed project. Some considered the bumps to be excessive, or inadequate, while others expressed concern over noise and bump location. A petition was available at the open house for residents along SE Clinton, from 12th to 21st Avenues, to sign and was circulated after the open house by a local resident. Petition results were as follows:
 
 
Category
Number
Percent of Total
Yes
39
69.6%
No
17
30.3%
Total
56
100%
 
Performance
 
Five 14-foot speed bumps, at 400 to 530 foot spacing, were constructed along the 0.44-mile length of SE Clinton, from 12th to 21st Avenues, on September 26, 1998 by Portland’s Bureau of Maintenance.
 
Vehicle Speeds
 
As graph one (next page) shows, vehicle speeds that previously peaked at 26 to 28 mphs now peak between 20 to 25 mphs. The average 85th percentile vehicle speed before the project was 33 mph. Since bump construction the average 85th percentile speed is 24.9 mph and ranges from a low of 18 mph (near a bump) to a high of 27 mph in the 25-mph zone. Before installation of the speed bumps 80% of drivers exceeded the posted speed limit of 25 mph and 10% exceeded the limit by 10 mph or more. Since bump construction 12% of drivers exceed the posted speed limit and 0.24% exceed the limit by 10 mph or more.
 
Graph 1
 
 
Traffic Volume
 
Traffic volumes measured before bump construction averaged 3400 vehicles per day (vpd). After bump construction volumes averaged 2300 vpd and varied from 2000 to 2700 vpd. This represents a 30% reduction, well above normal daily fluctuations. Traffic volumes measured on streets adjacent to SE Clinton, 12th to 21st Avenue, no significant increases from measurements before construction.
 
Conclusion
 
Traffic Calming on SE Clinton, 12th to 21st Avenues, has successfully reduced the average 85th percentile speed closer to the posted speed and also decreased the number of cars using the street.