Speed Cushions for the Evergreen Corridor Bike Lane Project

Vancouver, Washington

Prepared by John Manix, P.E., PTOE, Former Traffic Engineer, City of Vancouver, WA.

Background

Evergreen Boulevard in Vancouver, Washington, was a popular bike route and had great potential as a bike commuter route because it connects downtown and a large residential neighborhood. Community goals for the project were to improve bicycle safety and compatibility, enhance pedestrian access for persons with disabilities, slow traffic, and improve roadway aesthetics with the hope of spurring redevelopment. Speeding on Evergreen Boulevard was a common neighborhood complaint. Although the posted speed limit was 25 mi/h, the 85th percentile speed was 34 mi/h, with about 90 percent of motorists traveling over the speed limit.

The corridor project was broken down into phases. This case study focuses on Phase 1 from E. Reserve to Grand Boulevard. This segment of Evergreen Boulevard was 0.65 miles long and in three years, had relatively few motor vehicle collisions and no collisions involving bicyclists.

The project scope proposed installation of bike lanes on Evergreen Boulevard, but this required removal of all on-street parking. Knowing that parking removal would not be popular; staff proposed installation of bike lanes along with streetscape improvements to minimize the protests associated with the loss of parking. The streetscaping was supported by the local neighborhood association because it reinforced the goal to beautify the street.

After extensive public involvement, the consensus was to install bike lanes on most of Evergreen Boulevard, but to leave 26 on-street parking spaces on the three blocks in the commercial district. To enhance bicycle compatibility in this section with shared travel lanes and on-street parking, traffic calming was proposed. Traffic calming also had the benefit of addressing resident concerns with speeding on Evergreen Boulevard.

Countermeasures

Typical speed humps were ruled out based on the impacts to commercial transit service and fire department response time. Curb extensions were also ruled out because a previous traffic calming project on a popular bike route had generated many bicycle safety complaints associated with bicyclists being pinched between moving traffic and the curb extensions.

For some time, staff had considered the use of speed cushions as an alternative to speed humps to provide an effective traffic calming tool on arterial, collector, or local streets that served as emergency response routes.

Speed cushions are modified speed humps. The shape resembles a cushion or pillow placed in the roadway, but a speed cushion does not span the entire roadway or traffic lane. The intent is to slow most motor vehicles, but to allow wide wheel-based vehicles such as buses and fire trucks to drive over them with minimal impact.

In researching the topic, staff found examples in Sacramento, CA, and Austin, TX. Sacramento's experience with what they refer to as a "speed lump" was particularly important because their devices were designed for the same size of fire engine and commercial bus as used in Vancouver. Vancouver tested speed cushions using rubber speed hump components that could be assembled to match the Sacramento speed lump width of six feet.

These trials allowed the city to test several configurations related to the position of speed cushion in the street. For example, should one cushion be placed in the center of the roadway like Sacramento's speed lump, or should they be placed in the center of the travel lane? If in the lane, how far apart should adjacent cushions be?

With the fire department's endorsement of the rubber speed cushion, the city implemented two other traffic calming projects concurrently with the Evergreen Corridor bike lane project that used speed cushions. These projects were West 33rd Street from Main Street to Columbia Street, and Southeast 155th Avenue from Southeast Mill Plain Road to Southeast 1st Street. The before and after speed survey data from the three projects as well as one other is provided below.

Evaluation and Results

Before and after bike counts were found inconclusive due to small sample size, so the city used the Bicycle Compatibility Index: A Level of Service Concept (BCI) to evaluate the project's effect on bicycling on Evergreen Boulevard.

The neighborhood objective of a reduction in speeding was evaluated with a before and after speed survey, a traffic count, and a collision history review. The speed survey and traffic count data were collected via hose counters in the vicinity of the proposed traffic calming before and midway between speed cushions following installation. The traffic data were collected for one midweek day. This case study includes the results of evaluation of the three other speed cushion projects.

Evergreen Level of Service
The secondary performance measures were related to community goals not exclusively linked to bicycling. The neighborhood objective of a reduction in speeding was evaluated with a before and after speed survey, a traffic count, and a collision history review. The speed survey and traffic count data were collected via hose counters in the vicinity of the proposed traffic calming before and midway between speed cushions following installation. The traffic data were collected for one midweek day. This report includes the results of three other evaluations of speed cushion projects.

The LOS changed from a high D to a mid-level C with the addition of speed cushions. This minor change is significant because LOS of C was noted in BCI Manual as a benchmark for roadways where casual bicyclists are expected. As a popular recreational bikeway, this was a reasonable expectation for Evergreen Boulevard.

The bicycle LOS of B for the bike lane section confirmed staff efforts to keep the shared lane section as short as possible.

Speed Cushions
In all cases, the speed cushions significantly reduced the speed of vehicles and have likely reduced the number of collisions. Table 2 shows the results of the speed survey and collision history of the four streets with speed cushions. All locations had very consistent results.

The 85 percent speed decreased to 30 mi/h or less on all streets that had a 25 mi/h speed limit. More importantly, the percentage of motorists travelling at over 30 mi/h dropped dramatically (Table 2). The traffic volume on each of the streets with speed cushions dropped about 10 percent, but there were no complaints about traffic diversion on parallel routes.

The following information was gained from the trial with rubber humps and permanent installation of four projects:

• The proposed shape of a speed cushion matching the profile of the current speed hump three inches high and a 14-foot parabolic curve profile, six-feet-wide with side ramps of 12 feet (1:4 grade) could be traversed by a fire engine without significant impacts.
• Using a speed cushion less than six feet wide (one trial at 5.5 feet) significantly compromised effectiveness.
• Speed cushions should be spaced approximately 300 to 400 feet apart along a roadway to keep the 85 percent speed of traffic at or below 30 mi/h.
• If the street is narrower than 38 feet, then parking restrictions should be used in the vicinity of the speed cushion.
• The speed cushion should be positioned in the center of the travel lane so buses and fire engines can align over the center of the cushion and remain within the travel lane.
• The speed cushion should be used on straight sections of roadway for fire trucks to position over the hump. From the trial it appears that speed cushions installed on a horizontal curve will be of little benefit because the rear wheels do not track the same as the front.
• The gap between the speed cushions should be two feet.
• With the speed cushion centered in the travel lane and the marking centered over the cushion, the marking helps fire engine and bus drivers line up wheels to straddle the cushion.

Speed cushion design with pavement marking.

Conclusions and Recommendations

Adding speed cushions to Evergreen Boulevard increased the bicycle LOS to level C and allowed the city to address the commercial community's desire to maintain on-street parking. But if parking had significantly increased, the lower speeds and volumes would not have adequately compensated to maintain the bicycle LOS C (the BLOS evaluation methodology is more sensitive to changes in parking than the speed of traffic).

Thus, the use of speed cushions is not recommended as a replacement for bike lanes for long sections of roadway, but they were a valuable tool for ensuring that the total project was considered a success by multiple interests; in this case the businesses that valued parking, bicyclists that needed safe bicycle facilities, and transit operators and emergency responders who needed to maintain access.

Traffic calming remained controversial with some bicycle riders. The main concern with speed cushions relates to a loss of control caused by hitting the tapered side of the speed cushion near the gutter. If a speed cushion design can provide a clear wheel path through the speed cushion, this safety concern can be addressed.

Costs and Funding

Speed cushions (material and labor): $2,000 each.

The speed cushions were funded within a larger project that included a Federal Transportation Enhancement grant and local matching funds.

Contact

John Manix P.E. PTOE
Former Transportation Engineer
City of Vancouver