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, 21^st to 26^th 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 Local Service Streets.

 

SE Clinton, from 21st to 26^th Avenues, serves a mixed single family residence and commercial neighborhood. SE 21^st Avenue, to the west, is a Local Service street under Portland’s traffic street classification system. SE 26^th Avenue, at this project segment's east end, is a Neighborhood Collector street. Clinton was broken at 21^st as a project segment due to Tri-Met service between 21^st and 26^th Avenue. SE Clinton, from 21^st to 26^th Avenues, is fairly straight, but does have a small hill between 22^nd and 23^rd Avenue, and has parking, sidewalk and curb on both sides.

 

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 21st to 26^th 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	44	86.2%
No	7	13.8%
Total	51	100%

 

Two 22-foot speed bumps were constructed along the 0.24-mile length of SE Clinton, 21^st to 26^th, on September 26, 1998 by Portland’s Bureau of Maintenance.

 

As graph two (next page) shows, vehicle speeds, previously peaked between 23 to 25 mphs, now peak between 20 to 22 mphs. The average 85th percentile vehicle speed before the project was 25.6 mph. Since bump construction the average 85th percentile speed is 23.6 mph and ranges from a low of 21 mph (near a bump) to a high of 26 mph in the 25-mph zone. Before installation of the speed bumps 15% of drivers exceeded the posted speed limit of 25 mph. Since bump construction 7.8% of drivers exceed the posted speed limit.

 

 

Traffic volumes measured before bump construction averaged 3300 vehicles per day (vpd). After bump construction volumes averaged 2450 vpd and varied from 2380 to 2520 vpd. This represents a 25% reduction, well above the expected daily fluctuation of 10%. Traffic volume measurements at 16 locations adjacent to SE Clinton, identified three that had volume increases that warrant additional monitoring. Tibbets Street, east of 23^rd; and 25^thAvenue, south of Division and north of Powell, will be reevaluated to determine the nature of the traffic increase.

 

Note: follow-up counts showed the increase to be transient, requiring no further action.

 

Traffic Calming on SE Clinton, 21^st to 26^th has successfully reduced the average 85th percentile speed closer to the posted speed and reduced the number of cars using the street.