Speed Bumps And Speed Humps

Continued from…Reducing street area where motor traffic is given priority.

Slow Point Examples: Medians

Medians

Medians are islands located along the roadway centerline, separating opposing directions of traffic
movement. They can be either raised or flush with the level of the roadway surface. They can be expressed as painted pavement markings, raised concrete platforms, landscaped areas, or any of a variety of other design forms. Medians can provide special facilities to accommodate pedestrians and
bicyclists, especially at crossings of major roadways.

Design Considerations:
• Medians are most valuable on major, multi-lane roads that present safety problems for bicyclists
and pedestrians wishing to cross. The minimum central refuge width for safe use by those with
wheelchairs, bicycles, baby buggies, etc. is 1.6 meters (2 meters is desirable).
• Where medians are used as pedestrian and bicyclist refuges, internally illuminated bollards are suggested on the medians to facilitate quick and easy identification.
• Used in isolation, roadway medians do not have a significant impact in reducing vehicle speeds. For the purpose of slowing traffic, medians are generally used in conjunction with other devices, such as curb extensions or roadway lane narrowing.

Several caveats apply:
• To achieve meaningful speed reductions, the travel lane width reduction must be substantial and visually obvious. The slowing, however, is temporary; as soon as the roadway widens again, traffic resumes its normal speed.
• Bicyclists have been put at risk of being squeezed where insufficient room has been left between a central median and the adjacent curb. Experience shows that most drivers are unlikely to hold back in such instances to let bicyclists go through first. This threat is particularly serious on roads with high proportions of heavy vehicles.
• The contradiction between the need to reduce the roadway width sufficiently to lower motorist speeds, while at the same time leaving  enough room for bicyclists to ride safely, must be addressed. This may be achieved by reducing the roadway width to the minimum necessary for a bicyclist and a motorist to pass safely (i.e., 3.5 meters).

There are three suggestions:
• Introducing color or texture changes to the road surface material around the refuge area reminds motorist that a speed reduction is intended.
• White striping gives a visual impression that vehicles are confined to a narrower roadway than that created by the physical obstruction — adjacent areas exist that vehicles can run over, but these are not generally apparent to approaching drivers.
• In some cases, provide an alternate, cut-through route for the bicyclists.

Next… Slow Point Examples:Curb Extensions

Intersection Humps/Raised Intersections
continued from Raised Crosswalks

Intersection humps raise the roadway at the intersection, forming a type of “plateau” across the intersection, with a ramp on each approach.  The plateau is at curb level and can be enhanced through the use of distinctive surfacing such as pavement coloring, brickwork, or other pavements. In some cases, the distinction between roadway and sidewalk surfaces is blurred. If this is done, physical obstructions such as bollards or planters should be considered, restricting the area to which motor vehicles have access.

Design Considerations:
• Ramps should not exceed a maximum gradient of 16 percent.
• Raised and/or textured surfaces can be used to alert drivers to the need for particular care.
• Distinctive surfacing helps reinforce the concept of a “calmed” area and thus plays a part in reducing vehicle speeds.
• Distinctive surfacing materials should be skid-resistant, particularly on inclines.
• Ramps should be clearly marked to enable bicyclists to identify and anticipate them, particularly under conditions of poor visibility.
• Care must be taken so the visually impaired have adequate cues to identify the roadway’s location (e.g., tactile strips). Color contrasts will aid those who are partially sighted.

Next… Traffic Calming - Reducing Street Area Where Motor Vehicle Traffic is a Priority.

Raised Crosswalks

(Continued from Bumps, Humps, & Other Raised Pavement Areas)

Raised crosswalks are essentially broad, flat-topped speed humps that coincide with pedestrian crosswalks at street intersections. The crosswalks are raised above the level of the roadway to slow traffic, enhance crosswalk visibility, and make the crossing easier for pedestrians who may have difficulty stepping up and down curbs.

Raised Crosswalks Design Considerations:
• Can be constructed of brick, concrete block, colored asphalt or cement, with ramps striped for
better visibility.
• Raised crosswalks are applicable:
(1) On roadways with vehicular speeds perceived as being incompatible with the adjacent residential                       land uses.
(2) Where there is a significant number of pedestrian crossings.
(3) In conjunction with other traffic-calming devices, particularly entry treatments.
(4) On two-lane or fewer residential streets classified as either “local streets” or neighborhood
collector streets.”
(5) On roadways with 85th percentile speeds less than 45 mph.

Next… Intersection Humps/Raised Intersections