Engineering Term of the Month
RUNAWAY RAMP A runaway ramp or truck escape ramp “ is an emergency area located adjacent to a downgrade roadway to provide a location for out-of-control vehicles to slow and stop away from other vehicles on the road . 1 ” Truck escape ramps are not only for trucks , but are also for use by other vehicles when the vehicle has lost braking ability . These ramps are usually located mid-slope or near the bottom of a long , steep , downward slope . The need for a truck escape ramp is typically determined based on crash experience and engineering judgement .
There are generally three types of ramps that are used , which include gravity ramps , sandpile ramps and arrester bed ramps . Gravity ramps are sloped upward to allow gravity to slow the vehicle . Sandpile ramps are constructed with loose , dry sand that increases resistance to movement when driven into by a vehicle . Arrester bed ramps use loose aggregate ( bedded with rock in gravel ) to slow down the vehicle . Rows or mounds of barrels are sometimes used at the end of the ramp as a “ last chance ” device .
Publications are available for determining bed lengths that account for entry , speed , length of bed , grade of bed and bedding type .
Sources :
• 1 . Nevada DOT https :// www . dot . nv . gov / safety / roadway-safety-improvements / truck-escape-ramps
• Pennsylvania DOT , 13M ( DM-2 ) Chapter 17 – Emergency Escape Ramps