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97 berms be constructed to three times axle height for vehicles of 85 tons capacity of less; for vehicles larger than 85 tuns, the berms should be constructed to four times axle height. Berms must be constructed to slopes greater than 40°. When berms cannot be constructed to a significant state of compaction, as indi- cated by tire sinkage qualification tests, the size of the berm must be in- creased according to the included recom- mendations to properly restrain a runaway haulage vehicle. The choice of a particular guardrail design depends on the vehicle size, ve- locity, and angle of approach. Guardrail configurations were analyzed for their capability to redirect 35-, 85-, and 170- ton loaded haulage vehicles traveling up to 35 mph with a 60° approach angle. Al- though guardrails can redirect a large haulage vehicle, they are generally too expensive for normal haul road use and are restricted to permanent or narrow elevated roadways. Barriers eliminate the possibility of a vehicle vaulting a berm. The vehicle is either redirected or stopped by the bar- rier's near-vertical face. Rigid bar- riers are almost indestructible and can be reused, but because of their high ini- tial cost, their use is restricted to permanent or narrow elevated roadways, as in the case of guardrails. A berm constructed from a continuous line of large boulders was evaluated. A runaway vehicle is stopped by impacting and pushing the boulders along the road surface. Analysis shows that too large a boulder will cause excessive dam- age to the vehicle upon impact; however, a boulder of acceptable size requires a considerable push distance. Therefore, boulders are not considered to be an ef- fective restraint system unless they are buried in an earthen berm. Median berms are sometimes placed in the center of a haul road to act as an additional restraining system. Analysis shows that a narrow compacted median berm is recommended over a wide median berm because it provides a shorter stopping distance and a reduced rollover potential when straddled by the runaway haulage vehicle. Escape lanes are the best restraining system because they can stop a vehicle without rolling it over and without dam- aging it. The escape lane should be 25 pct wider than the truck and be con- structed of loose draining gravel, with a depth that varies from a minimum at the entrance to twice the truck's ground clearance at the vehicle's estimated stopping distance to prevent abrupt stops and rollback. eU.S. GPO 1984 545 OHI5~60 INT: 9U.OF MIN ES,P GM.,P d, 2)086