Traffic Calming Measures

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Traffic Calming Measures

Traffic Circle
Traffic circles are raised islands, placed in intersections, around which traffic circulates. They are usually circular in shape and nearly always landscaped in the center. Circles prevent drivers from speeding through intersections by restricting the straight-through movement. Drivers must weave around the circle and may easily do so without impeding pedestrian space.

Speed Hump
A speed hump is a raised area in the roadway pavement surface extending transversely across the travel way. It is 3 inches high and 14 feet long, extending to either the curb or the edge of the parking area. The speed hump would be marked with bold white "v" markings and would have an appropriate sign preceding the hump to warn drivers that they are approaching the measure.

Speed Table
A speed table is a raised area in the roadway pavement surface extending transversely across the travel way. It is 3 inches high and 22 feet long, extending to either the curb or the edge of the parking area. The speed table would be marked similarly to a speed hump and include appropriate warning signage. This measure is designed for a larger vehicle and to provide a gentler ride to passenger vehicles.

Speed Cushion
A speed cushion is a raised area in the roadway pavement surface extending transversely across the travel way. It is 3 inches high and 14 feet long, extending to either the curb or the edge of the parking area, but unlike the speed hump, it has 2 one-foot slots which allow large wheel based vehicles such as Muni buses to pass over without being affected by the measure.

Tests & Results

DPT, with the cooperation of the San Francisco Fire Department, Municipal Railway (Muni), the Mayor's Office on Disability (MOD), and the Physical Access Committee of the Mayor's Disability Council (MDC), tested a variety of traffic calming measures. It was not deemed necessary for the Fire Department to test the rumble strips or speed lumps. Similarly, Muni did not test the rumble strips. The MOD tested all of the measures, while due to time constraints, the MDC did not test speed lumps.

Traffic Circles
The traffic circle tested is located at the intersection of Urbano Drive and Victoria Street. The perimeter of the circle is a 6-inch concrete curb. The center asphalt layer was removed and filled in with earth, which was landscaped with flowers and various low-growing shrubs. The test vehicles tested their maneuverability around the circle.

The Fire Department has no objections to the installation of traffic circles on City streets. Muni does have some minor concerns about maneuverability around the traffic circles, but are willing to test future designs. While both MOD and MDC have some minor concerns about pedestrian safety, the MDC supports the use of traffic circles as part of our Traffic Calming Program.

Speed Humps
There are four speed humps located in the West Clay Park neighborhood. One on 24th Avenue, between Lake and West Clay Streets, two on West Clay Street, between 22nd and 24th Avenues, and one on 22nd Avenue, between Lake and West Clay Streets. The speed humps are made from recycled tires. Test vehicles drove over the speed humps at varying speeds starting at 5 miles per hour (mph) to an upper limit of 25 mph, increasing their speed in 5 mph increments.

The Fire Department does not object to the installation of speed humps on City streets. Due to the jolting to their buses as they drive over a speed hump, Muni requests that speed humps are not installed on their routes. MOD stated in their report, "Because of it's design (height/width), this particular measure has the most negative effect on vehicle passengers. This measure of traffic calming device creates a very jarring ride, especially for passengers of paratransit vehicles who are typically sitting in the back of the vehicle". MOD recommends that the maximum safe speed for this system is 5 mph and requests large speed limit signs. MDC stated in their report, "These traffic measures are very much like the speed bumps in that 5 mph is the only safe speed that would cause the least amount of discomfort. Getting drivers of paratransit vans to abide by lower speeds would, in my view, be very difficult."

Speed Table
A speed table was temporarily installed in the parking lot of Candlestick Park. The speed table tested was constructed from recycled tires. For the test, vehicles drove over the speed table at varying speeds starting at 5 mph to an upper limit 25 mph, increasing their speed in 5 mph increments.

The Fire Department does not object to the installation of speed tables on City streets. In their report, Muni stated that at speeds above 10 mph, the speed table caused an extremely bumpy ride, similar to a "roller coaster". Due to this "roller coaster" effect, they are concerned for the safety of their passengers. They are also concerned about the structural damage that may occur to their buses as they pass over the speed table. Consequently, they request that speed tables are not installed on their routes. MOD stated in their report, "While this system proved to be the least intrusive, 25 mph was unacceptable". MOD suggests the possible reduction in height of the speed table and have a maximum speed limit, suggested 10 mph, posted with a warning about the speed table. In their report the MDC stated, "This device at 5 mph and 10 mph was like riding in a van on any street in San Francisco. At the higher speeds it was unbearable for a person with a spinal injury." They also suggest large signage or additional painting.

Speed Lumps
The speed lump tested was temporarily installed on Middle Drive West, between Transverse Drive and Overlook Drive, within Golden Gate Park. The speed lump tested was constructed from recycled tires. For the test, vehicles drove over the speed table at varying speeds starting at 5 mph to an upper limit 25 mph, increasing their speed in 5 mph increments.

Muni does not object to the installation of the speed lump on City streets. MOD does not approve of the installation of the speed lump.

Rumble Strips
The rumble strips tested are constructed from ceramic markers. The test site for the rumble strips was West Pacific Avenue, west of Presidio Boulevard, within the Presidio. The test vehicles drove over this system at approximately 5 to 10 mph. This particular site has 3 rows of ceramic markers crossing the street.

MOD stated, "Design the installation of this system with a maximum of 2-3 rows". MDC stated that "This system was the least invasive, while the site only had three rows, additional rows probably would increase the discomfort."

General comments from the disability community on the vertical displacement measures:

MOD stated in their report that "Many in the disabled community have the type of disability (typically nerve damage) that is negatively affected by vertical traffic calming measures which affect the ride of the vehicle they are in. In a paratransit vehicle, the passenger has no control over how fast the driver operates the vehicle and therefore, cannot stop the driver from using an inappropriate speed." MDC has adopted a resolution opposing the installation of vertical deflection traffic calming measures (Item 12 in Minutes of July 20, 2001 Mayor's Disability Council meeting).

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