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Urban Street Design Guide Index

Urban Street Design Guide
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Vertical Speed Control Elements

Vertical Speed Control Elements

Vertical speed control elements manage traffic speeds and reinforce pedestrian-friendly, safe speeds. These devices may be appropriate on a range of street types, but are most widely applied along neighborhood, residential, or low-speed streets where freight traffic is discouraged.

They may be installed in tandem with horizontal traffic calming measures such as curb extensions or chicanes, or applied individually on streets with a constrained right-of-way.

Vertical speed control has been shown to slow traffic speeds, creating a safer and more attractive environment.

Application

Vertical speed control elements should be applied where the target speed of the roadway cannot be achieved through the use of conventional traffic calming elements, such as medians, narrower roadways or lanes, curb extensions, enforcement or lower speed limits.
Streets with speed limits of 30 mph and under are good candidates for vertical speed control, especially where those streets have higher than desired operating speeds or are used by cut-through traffic on a regular basis.

See Neighborhood Street

Benefits & Considerations

Vertical speed control has been shown to slow traffic speeds, creating a safer and more attractive environment.1
Vertical speed control elements are most effectively implemented at a neighborhood level, rather than by request on a single street. Designate “Slow Zones” where traffic calming treatments should be targeted or coordinated in a comprehensive way.2
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New York City's application-based neighborhood slow zone program targets traffic calming investments and speed control in defined low-speed areas.
In colder climates, vertical traffic calming must be designed to permit snow removal. Cities must work cooperatively with local agencies responsible for street-sweeping and snow-removal to ensure that they do not significantly hinder operations or damage speed control elements.
Vertical speed control elements may deter cut-through traffic but exacerbate traffic conditions on surrounding streets as a result. Monitor the impact of traffic calming treatments at the network level or install on a pilot basis to assess potential impacts.
Unless otherwise desired, vertical traffic calming should reduce a street’s target speed to 20 mph or less.
Implementation may be carried out on a trial basis to gauge residents’ support prior to finalizing the design. Temporary speed humps, tables, and cushions should be used with caution as they can diminish residents’ opinions due to unappealing design and reduced functionality.
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The ideal spacing for vertical speed controls depends on the specific profile of the street, as well as horizontal or regulatory traffic calming measures. Spacing should be consistent and determined according to the desired target speed and operating speed of the road, as well as volume, context, and the overall number of driveways. Where drivers accelerate to unsafe speeds between speed controls, spacing may need to be reevaluated.

Footnotes

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  1. For example, many speed hump programs prepare by clocking vehicle speeds and determining the 85th percentile speeds in relation to the desired speed before installation takes place.

    City of Redwood City Policy and Guidelines for Speed Hump Use (Redwood: Redwood City Community Development Services, 1997).

  2. NYC DOT takes applications for Slow Zones, projects that reduce the speed limit from 30 to 20 mph in residential areas, adding design and signage elements that enforce these lower speeds. Slow Zones typically measure 5 blocks by 5 blocks, or a quarter square mile.

    “Neighborhood Slow Zones,” New York City Department of Transportation, accessed June 3, 2013.

References

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Adapted from the Urban Street Design Guide, published by Island Press.

Subsections:

Speed Hump

Speed Hump

Speed humps are parabolic vertical traffic calming devices intended to slow traffic speeds on low volume, low speed roads. Speed humps are 3–4 inches high and 12–14 feet wide, with a ramp length of 3–6 feet, depending on target speed.

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Speed Table

Speed Table

Speed tables are midblock traffic calming devices that raise the entire wheelbase of a vehicle to reduce its traffic speed. Speed tables are longer than speed humps and flat-topped, with a height of 3–3.5 inches and a length of 22

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Speed Cushion

Speed Cushion

Speed cushions are either speed humps or speed tables that include wheel cutouts to allow large vehicles to pass unaffected, while reducing passenger car speeds. They can be offset to allow unimpeded passage by emergency vehicles and are typically used

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References

References for Vertical Speed Control Elements: 22 found.