Horizontal Displacement

The following devices are generally applicable only on streets at least 36 feet wide:

• Roundabouts (Traffic Circles) - raised circular islands placed in the center of an intersection (generally four leg intersection). They are designed to have a slowing effect on vehicles in a range of 200 to 500 feet and to control right of way at the intersection (approaching vehicles must yield to traffic in the circle). All vehicles except emergency vehicles must travel to the right of and counterclockwise around the circle.
• Curb extensions - narrow the street by widening the sidewalk/grass strip area. These can be placed at an intersection or mid-block. At mid-block locations, they will eliminate some parking. They can be a safety benefit for pedestrians in that there is a shorter crossing distance and better visibility. They are most effective the greater the lateral displacement of the vehicle that can be achieved (e.g., creation of a serpentine alignment.).
• Median or pedestrian refuge islands - raised islands placed the middle of the road displacing a vehicle to the right. These can be oval or elliptical shaped. Those islands used at a crosswalk to provide a pedestrian refuge increase pedestrian safety by allowing pedestrians to cross one direction of traffic flow at a time.
• Edgelines - white pavement lines typically placed approximately 8 feet from the pavement edge narrowing the traveled portion of the roadway by creating a parking lane or shoulder area. May be used with or without a centerline and in conjunction with chokers. (Edgelines are not considered an actual physical device, but are used to visually create a channelizing effect).

 

The following devices are applicable on most width streets:

• Speed Humps - 3 inches high, parabolic or flat-topped raised pavement, typically 12 or 22 feet long in the direction of travel, and generally spaced approximately every 500 feet (however, may be as much as 750 feet). Humps are generally only applicable on streets with direct residential frontage and with posted speed limits of 25 or 30 MPH. An attempt is made to locate humps at property lines --they are not installed on sharp curves or hillcrests where visibility may be restricted, on steep grades, in intersections or at driveways. Humps are designed to allow snow plowing and accommodate larger vehicles such as school buses and fire trucks.
• Raised intersections or crosswalks - similar to flat top speed humps but typically spaced over a longer distance. Used to slow vehicles, as well as to indicate to motorists that they are entering a residential area or to emphasize a crosswalk location.

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