Runaway truck ramp

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A runaway truck ramp on U.S. Route 60, before a left turn.
A runaway truck ramp on U.S. Route 60, before a left turn.
An arrester bed in Western Australia, located at the bottom of a hill before an intersection.
An arrester bed in Western Australia, located at the bottom of a hill before an intersection.

A runaway truck ramp, runaway truck lane, emergency escape ramp or truck arrester bed is a traffic device that enables vehicles that are having braking problems to safely stop. It is typically a long, gravel-filled lane adjacent to a road with a steep grade, and is designed to accommodate large trucks. The deep gravel allows the truck's momentum to be dissipated in a controlled and relatively harmless way, allowing the operator to stop it safely.

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[edit] Design

Emergency escape ramps are typically located in mountainous areas which attract high construction costs and present difficult site selection.[1] Designs include:

  • Arrester bed (see below): a gravel-filled ramp adjacent to the road that uses rolling resistance to stop the vehicle.
  • Gravity escape ramp: a long upwardly-inclined path parallel to the road. A large length is required, control can be difficult for the driver, including rollback after the vehicle stops.
  • Sand pile escape ramp: a short length of loosely piled sand. Problems include large deceleration and the sand being affected by weather conditions (moisture and freezing).
  • Alternatives: such as a vehicle arresting barrier.[2]

[edit] Location

Emergency escape ramps are usually located on steep, sustained grades, as in mountainous areas.[1] Long descending grades allow high vehicle speeds to be reached, and truck brakes can overheat and fail through extensive use. The ramps are often built before a critical change in the curvature of the road, or before a place that may require the vehicle to stop, such as before an intersection in a populated area.[2]

[edit] Arrester bed

An arrester bed usually uses gravel/aggregate that imparts a rolling resistance on the vehicle that enters the bed.[1] The required length of the bed depends on the mass and speed of the vehicle, the grade of the arrester bed, and the rolling resistance provided by the gravel.[2]

[edit] References

  1. ^ a b c DOT Arizona (May-June 1993). "Full-Scale Arrester Bed Testing Leads to More Cost-Effective Design" (pdf). TR News (166): 20–21. 
  2. ^ a b c (May 2006) Design Manual - Auxiliary Lanes (pdf), Washington State Department of Transportation, Chapter 1010, pp. 4-5. 

[edit] External links

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