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, 26^th to 39^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 low-volume Local Service Streets.

 

SE Clinton, from 26^th to 39^th Avenues, serves a mixed single family residence and commercial neighborhood. SE 26^th Avenue, to the west, is a Neighborhood Collector street under Portland’s traffic street classification system. SE 39^th Avenue, at this project segment's east end, is a Major City Traffic street. SE Clinton, from 26^th to 39^th Avenues, has a horizontal curve from 26^th to 27^th and a slight hill before leveling off at 28^th Avenue. The street 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. Forty-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 to sign and was circulated after the open house by a local resident. Petition results were as follows:

 

Category	Number	Percent of Total
Yes	96	77.4%
No	28	22.6%
Total	124	100%

 

Nine 14-foot speed bumps, at 320 to 600 foot spacing, were constructed along the 0.83-mile length of SE Clinton, 26^th to 39^th Avenues, on September 26 and October 18, 1998 by Portland’s Bureau of Maintenance.

 

As graphs three through five show (next page), vehicle speeds that previously peaked at 26 to 28 mph, now peak at 23 to 25 mph. The average 85th percentile vehicle speed before the project was 31 mph. Since bump construction the average 85th percentile speed is 25.1 mph and ranges from a low of 19 mph (near a bump) to a high of 28 mph in the 25-mph zone. Before installation of the speed bumps 58% of drivers exceeded the posted speed limit of 25 mph and 8% exceeded the limit by 10 mph or more. Since bump construction 15% of drivers exceed the posted speed limit and 0.3% exceed the limit by 10 mph or more.

 

 

 

 

 

 

 

Traffic Volume

 

Traffic volumes measured before bump construction averaged 2590 vehicles per day (vpd). After bump construction volumes averaged 1870 vpd and varied from 2270 at the west end, to 1260 at the east end of the project segment. This pattern of traffic matches the pattern measured before construction. Traffic volume measurements at 24 locations on streets in the neighborhood around SE Clinton, 26^th to 39^th Avenues, identified one with volume increases that warrant additional monitoring. SE 28^th, north of Powell, will be reevaluated to determine the nature of the volume increase.

 

Traffic Calming on SE Clinton, 26^th to 39^th Avenues, has successfully reduced the average 85th percentile speed closer to the posted speed and also decreased the number of cars using the street.