Runaway truck ramp

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, 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

Emergency escape ramps are typically located in mountainous areas which attract high construction costs and present difficult site selection.cite journal
author = DOT Arizona | year = 1993 | month = May-June | title = Full-Scale Arrester Bed Testing Leads to More Cost-Effective Design | journal = TR News | issue = 166 | pages = 20–21 | url = http://www.trb.org/publications/trnews/rpo/rpo.trn166.pdf | format = pdf | accessdate = 2006-07-23] Designs include:

Type overview

*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.cite book | month = May | year = 2006 | title = Design Manual - Auxiliary Lanes | publisher = Washington State Department of Transportation | pages = Chapter 1010, pp. 4-5 | url = http://www.wsdot.wa.gov/EESC/Design/ DesignManual/desEnglish/1010-E.pdf | format = pdf]

Arrester bed

An arrester bed usually uses gravel/aggregate that imparts a rolling resistance on the vehicle that enters the bed. 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.

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.

References

External links

* [http://www.webs1.uidaho.edu/niatt_labmanual/Chapters/ geometricdesign/professionalpractice/DescendingGrades.htm Design considerations]
* [http://www.usroads.com/journals/rej/9708/re970801.htm Truck escape ramps from www.usroads.com]
* [http://magpie.lboro.ac.uk/dspace/ bitstream/2134/2205/1/VS1539+AR2517.pdf European road design (search for "arrester bed")]