One of the best and most frequently used mechanisms for stopping runaway trucks is the truck escape ramp, in particular the gravel arrester bed. To learn more about the energy absorbing characteristics of the stone and to develop better design criteria, the Ppennsylvania Ttransportation Iinstitute (PTI) is conducting full-scale testing of gravel arrester beds. This paper presents a summary of the data taken for the first-year tests, the methods used for data reduction and analysis, some conclusions based on these initial tests, and recommendations for future testing. For this study, PTI constructed two 300-ft-long test ramps, one filled with rounded river-bed-gravel and the other with more angular crushed gravel. Eleven tests were performed in 1984 using an international fleetstar dump truck as the test vehicle. Seven tests were in crushed gravel, three in river gravel, and one at a newly constructed ramp in Punxsutawney, pa., which also contained the same river gravel as in the PTI bed. The data taken included entry speed, stopping distance, accelerometer data, cross-section measurements of the ruts left by the truck tires, and distance vs time data. The river gravel exhibited greater tire penetration and volume of stones displaced, along with greater deceleration forces than the crushed gravel. The Punxsutawney test represented the standard of excellence, showing an average deceleration of 0.516 g due to its larger gravel depth. Other results showed that loading the truck did not affect the stopping distance in crushed gravel. (author/publisher).
Abstract