Runaway truck ramp
Encyclopedia
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
-filled lane adjacent to a road with a steep grade, and is designed to accommodate large truck
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...
s. 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
Emergency escape ramps are typically located in mountainous areas which attract high construction costs and present difficult site selection. Designs include:Type overview
- Arrester bed (see below): a gravel-filled ramp adjacent to the road that uses rolling resistanceRolling resistanceRolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. It is caused mainly by the deformation of the object, the deformation of the surface, or...
to stop the vehicle. 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. - 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 and the sand being affected by weather conditions (moisture and freezing).
- Alternatives: such as a vehicle arresting barrier.
Location
Emergency escape ramps are usually located on steep, sustained grades, as in mountainous areas. 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.These can vary from one state to another however.