Bumps, Humps, & Other Raised Pavement Areas.
Speed Bumps and Humps are included in the category that includes all traffic-calming devices raised above pavement level. Drivers have no other choice than to slow down when they cross these devices or suffer an uncomfortable KER-BUMP or (KER-BUMP-KER-BUMP), running the risk of spilled coffee and a severe jolt to their tailbones. Although people often gripe about the inconvenience of having to slow down for these devices, they don’t have much choice. Their effectiveness at slowing traffic cannot be disputed. They are sometimes referred to as “Silent Policemen.”
Included in this category are:
• Speed bumps.
• Speed humps.
• Raised crosswalks.
• Raised intersections.
Speed Bumps
A speed bump is a raised area in the roadway pavement surface extending transversely across the travel way, generally with a height of 3 to 6 inches and a length of 1 to 3 feet.
Speed Bump Design Considerations:
• Most effective if used in a series at 300- to 500- foot spacing.
• Typically used on private property for speed control – parking lots, apartment complexes, private streets, and driveways.
• Speed bumps are not conducive to bicycle travel, so they should be used carefully.
Speed Humps
A speed hump (or “road hump”) is a raised area in the roadway pavement surface extending transversely across the roadway. Speed humps normally have a minimum height of 3 to 4 inches and a travel length of approximately 12 feet, although these dimensions may vary. In some cases, the speed hump may raise the roadway surface to the height of the adjacent curb for a short distance. The humps can be round or flat-topped.
The flat-topped configuration is sometimes called a “speed table.” Humps can either extend the full width of the road, curb-to-curb, or be cut back at the sides to allow bicycles to pass and facilitate drainage.
Speed Hump Design Considerations:
• If mid-block pedestrian crossings exist or are planned, they can be coordinated with speed hump installation since vehicle speeds will be lowest at the hump to negotiate ramps or curbs between the sidewalk and the street.
• The hump must be visible at night.
• Speed humps should be located to avoid conflict with underground utility access to boxes, vaults, and sewers.
• Speed humps should not be constructed at driveway locations.
• Speed humps may be constructed on streets without curbs, but steps should be taken to prevent circumnavigation around the humps in these situations.
• Adequate signing and marking of each speed hump is essential to warn roadway users of the hump’s presence and guide their subsequent movements.
• Speed humps should not be installed in street sections where transit vehicles must transition between the travel lane and curbside stop. To the extent possible, speed humps should be located to ensure that transit vehicles can traverse the hump perpendicularly.
• A single hump acts as only a point speed control. To reduce speeds along an extended section of street, a series of humps is usually needed. Typically, speed humps are spaced at between 300 and 600 feet apart.
Speed Hump Real Life Example:
Bellevue, Washington has installed speed humps in residential neighborhoods (labeled as speed “bumps” below, although broader than the typical speed bump). The City uses a 12-foot-wide hump, 3 inches high at the center. The design allows for little or no discomfort at speeds of 15 to 25 mph, but will cause discomfort at higher speeds. The humps are marked clearly, distinguishing them from crosswalks. White reflectors enhance nighttime visibility. Bellevue found that the speed humps reduced traffic speeds and volumes. The humps, in general, received strong public support, and residents favored their permanent installation.
The following concerns were raised regarding the speed hump installation:
• Concern about restricted access and increased response time for emergency vehicles. The Bellevue Fire Department asked that the humps be installed on primary emergency access routes.
• Concern about aesthetics of signing and markings at the traffic humps. Residents raising the concerns, however, felt that the speed reductions compensated for the appearance of the humps.
• Concern about the effectiveness of the humps in reducing motor vehicle speeds along the length of a street, not at just two or three points. The distance between speed humps was found to
have an impact on traffic speeds. The City found that maximum spacing should be approximately
500 feet.
The Bellevue Department of Public Works concluded that speed humps were effective speed-control measures on residential streets and recommended their use be continued.
Next… Raised Crosswalks
