The Traffic Calming Program (TCP) undertook a traffic calming project in the fall of 1995 to address traffic problems identified by residents along SW 35th Avenue from Vermont to Capitol Highway.
The land uses along SW 35th Avenue are primarily single-family residential. SW Vermont, to the north, is classified as a "Neighborhood Collector" in the Transportation Element of the Comprehensive Plan (TE). SW Capitol Highway, at SW 35th Avenue's south end, is classified as a "District Collector," and SW 35th Avenue is classified as a "Local Service" street. "Local Service" streets, by City policy, are intended to primarily serve the properties located along them. A typical "Local Service" street carries a traffic volume between 500 - 1,500 vehicles per day. A large portion of the daily traffic on SW 35th Avenue is believed to be cut-through traffic due to 1) a traffic signal at Multnomah Boulevard, two blocks south of Capitol Highway, 2) a lack of nearby collector and local streets parallel to SW 35th Avenue, and 3) Multnomah Village, a compact commercial development at Capitol Highway.
The project portion of SW 35th Avenue is from SW Vermont to SW Capitol Hwy. SW 35th Avenue has two lanes of travel, with parking permitted on both sides of the street. The street pavement width is approximately 20 feet wide. There are no curbs or sidewalks on either side of the street. Additionally, there are vertical curves which limit sight distances. There are eight "Local Service" streets which intersect SW 35th Avenue, some of which are "T" intersections. These streets are stop-controlled.
There is a Tri-Met bus that travels on this project portion of SW 35th Avenue. SW 35th Avenue is designated as a Bike and Pedestrian Route in the TE. SW 35th Avenue was identified as a primary fire response route before this project was begun. Fire route designation will be further discussed under "Project History."
The first meeting held for this project was in November 1995. Twenty-five people attended this first meeting, and 18 of them volunteered on an advisory committee to work with staff to develop goals and objectives, and define the project elements. Committee membership was open to anyone with an interest in the project.
At that time the Fire Bureau and Bureau of Traffic Management were conducting tests to determine the impact of traffic calming devices on fire vehicles. The testing and discussion between the two bureaus became more complex, and it was at this time that the SW 35th Avenue project was put on hold pending the outcome of those discussions. It was ultimately determined, at the City Council level, that traffic calming projects on fire response routes would be on hold until a new emergency route designation is developed according to and incorporated into the TE. Developing this new classification was expected to take up to 2 years until implemented.
Residents on SW 35th Avenue questioned the need to wait another 2 years for their project. Staff and residents recognized that the only devices that would help solve their traffic problem would be speed bumps. They believed their street was not an appropriate primary fire response route, and if it remained one, speed bumps may never be used. They conducted their own timed tests from both fire stations serving that area; they found that the fire vehicles did not need SW 35th Avenue to stay within their desired 4-minute response. After further discussions and analysis between the residents, the Fire Bureau, and the Bureau of Traffic Management, in October 1996, the Fire Bureau agreed to take SW 35th Avenue off the Fire Bureau Response Map.
In November 1996, 1 year after the first meeting for this project, the second meeting for the SW 35th Avenue traffic calming project was held. It was at this meeting that traffic calming options were discussed. Both Tri-Met and Fire Bureau representatives expressed their preference for 22-foot speed bumps over the 14-foot speed bumps. While diversion was considered, it was quickly ruled out because of the greater impact any diversion would have in the area around SW 35th. Residents reiterated that their primary problem was speeding, and that they could deal with the volume if it was traveling slower.
Three different speed bump design options were presented. One option had six bumps; others had four, placed in different locations. While the Fire Bureau expressed their preference for the fewer number of bumps, they were also concerned about the location of one bump near the bottom of a hill. They were concerned that slowing for the bump would make it harder for them to accelerate to get up the hill. Finally, the committee chose an alternative that consisted of five speed bumps. Since this was not a presented option, staff said it would design a five-bump plan, taking into account the Fire Bureau's concerns.
Residents along SW 35th Avenue, and the surrounding neighborhood, were invited to an open house to review and comment on the proposed speed bump installation. As required by the TCP process, a mail ballot was conducted by the Bureau of Traffic Management. A majority of the ballots returned favored the project. Eligible voters included all residents, businesses and property owners within the area likely to receive significant benefits or disadvantages from the project. A breakdown of the vote is shown on the next page.
SW 35TH AVENUE TCP BALLOT RESULTS
# of Valid Ballots: 105
# of Ballots Returned: 85
% Returned: 81%
# of Yes Votes: 64
# of No Votes: 21
% of Votes in Favor: 75%
Five 22-foot speed bumps, at 420 to 820 foot spacing, were constructed along the 0.53 mile length of SW 35th Avenue, Vermont to Capitol Highway, on October 18, 1997 by Portland's Bureau of Maintenance.
Graph 1. Change in Speed Distribution
As Graph 1 shows, vehicle speeds, previously concentrated between 26 and 31 mph, have been shifted into the range of 23 to 28 mph between the speed bumps. The average 85th percentile vehicle speed before the project was 32.3 mph. Since bump construction the average 85th percentile speed is 27.6 mph when not including speeds counts taken on the hills. If the speeds of vehicles on the hills are included, the average 85th percentile speed becomes 31 mph. If a device existed that could be built on the hills, the 27.6 mph speed would be the most accurate measure of vehicle slowing. Vehicle speeds range from a low of 24 mph (near the bumps) to a high of 42 mph on a hill. Before installation of the speed bumps 67% of drivers exceeded the posted speed limit of 25 mph and 7.6% exceeded the limit by 10 mph or more. Since bump construction 45% of drivers exceed the posted speed limit and 5% exceed the limit by 10 mph or more. A greater decrease in vehicle speed was not possible due to the use of 22 foot speed bumps necessitated by transit and fire response concerns. The 22 foot speed bumps are intended to reduce average vehicle speeds along a street into the range of 28 to 32 mph, and appear to be achieving this goal.
Traffic volumes measured before bump construction averaged 1820 vehicles per day (vpd) and varied from 1290 to 2140 vpd, including weekends. If weekend data is excluded, traffic volumes measured before bump construction averaged 1960 vehicles per day (vpd) and varied from 1650 to 2140 vpd. After bump construction volumes averaged 1700 vpd and varied from 1620 to 1900 vpd.
Graphs 2-4 show the change, over a 24-hour period, for the northbound, southbound and total traffic volume, respectively. The most apparent change is the reduction in northbound morning and lunch time vehicles.
Neighborhood Traffic Volume
Table 1, below, shows traffic volumes measured on streets around SW 35th Avenue before and after speed bump construction. Streets listed in bold print are collector streets where volume increases are not limited.
Table 1. Neighborhood Volume Changes
|SW 32nd, North of Capitol Hwy||271||272||1||0|
|SW 33rd, North of Capitol Hwy||318||270||-48||-15%|
|SW 34th, South of Vermont||157||105||-52||-33%|
|SW 34th, South of Miles||356||267||-89||-25%|
|SW 45th, North of Multnomah||6,421||7,290||869||13%|
|SW Troy, East of 40th||1,508||1,495||-13||0|
|SW Vermont, West of 35th||7,902||8,795||893||11%|
|SW Vermont, East of 35th||8,940||8,935||-5||0|
|SW Capitol Hwy, East of 31st||10,006||10,328||322||3%|
From Table 1, it can be seen that traffic volumes measured on local streets around SW 35th Avenue all had measured decreases. The measurements also indicate that traffic has increased on Vermont, west of 35th, on SW 45th, and on Capitol Highway. Each of these streets are classified as Neighborhood Collector streets, or higher, in the city's Comprehensive Plan and are more appropriate routes for general traffic than is SW 35th. In comparing the traffic volumes measured on SW 35th and the measurements for streets surrounding SW 35th, it appears that some traffic has chosen to move to the collector streets.
The SW 35th Avenue Traffic Calming Project has succeeded in reducing vehicle speeding, especially where speed bumps could be constructed at standard spacing. Traffic volume on SW 35th appears to have slightly reduced without diverting to nearby local service streets. By these standards, traffic calming on SW 35th Avenue, Vermont to Capitol Highway, has enhanced street safety and livability and can be considered successful.