Runaway truck ramp

A runaway truck ramp, runaway truck lane, escape lane, emergency escape ramp, or truck arrester bed is a traffic device that enables vehicles which are having braking problems to safely stop. It is typically a long, sand- or gravel-filled lane connected to a steep downhill grade section of a main road, and is designed to accommodate large trucks or buses. The ramp allows a moving vehicle's kinetic energy to be dissipated gradually in a controlled and relatively harmless way, helping the operator to stop it safely without a violent crash.
Design.
Emergency escape ramps are usually located in mountainous areas which cause high construction costs and present difficult site selection. A ramp may cost US$1 million. Designs include:
Location.
Emergency escape ramps are usually located on steep, sustained grades, as in mountainous areas. Long descending grades can 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 radius of curvature of the road, or before a place that may require the vehicle to stop, such as before an intersection in a populated area. 
The placement criteria can vary from one region/country to another.