Runaway truck ramp

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A runaway truck ramp, runaway truck lane, escape 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, sand or 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.

Design[edit]

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

  • Arrester bed: a gravel-filled ramp adjacent to the road that uses rolling resistance to stop the vehicle.[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]
  • Gravity escape ramp: a long upwardly-inclined path parallel to the road. A large length is required. Control can be difficult for the driver: problems include rollback after the vehicle stops.
  • Sand pile escape ramp: a short length of loosely piled sand. Problems include large deceleration; sand being affected by weather conditions (moisture and freezing), and; vehicles vaulting and/or overturning after contacting the sand pile.
  • Mechanical-arrestor escape ramp: a proprietary system of stainless-steel nets transversely spanning a paved ramp that engage and retard a runaway vehicle. Ramps of this type are typically shorter than gravity ramps and can have a downhill grade. One such ramp at Avon, Connecticut in the United States has an electrically-heated pavement surface to prevent snow and ice accumulation.[3][4]
  • Alternatives: such as a vehicle arresting barrier.[2]

Location[edit]

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] These can vary from one region/country to another however.

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