There you are, driving your rig down a mountain pass—loaded to the legal max of 80,000 pounds—grooving to Little Feat’s “Willin’.” Suddenly, you notice your speed getting away from you, but you can’t downshift your nonsynchro tranny. You hit the brakes, but they’re fading. They, like 95 percent of all heavy-truck brakes, are drums. You’re in trouble.

What saves the bacon you’re hauling is an exit to the right: a gravel-covered off-ramp that leads up a rise or hill, eliminating the need for brakes. Six (eternal) seconds later, you are almost stopped... and glad you wore your brown pants.

Here’s what you need to know about runaway ramps, even if you don’t drive a big rig:

• Also called “truck escape ramps”—or in Britain, “escape bays”—they rely on the additional friction created by gravel or sand and, usually, the gravitational slow-down effect of an incline to stop runaway vehicles. Aircraft-carrier-type arresting cables with netting have been used in lieu of ramps, but they require more maintenance.

• While no one seems to know when or where the ramps first appeared, the consensus is some time in the mid-’60s, appropriately, in mountainous regions.

• By 1990, there were reportedly 170 runaway ramps in 27 (mostly western) states. Current data is scarce, but a 1981 NHTSA study notes there had been 2450 runaway-truck incidents that year, with 2150 of those involving the use of ramps.

• If properly built, runaway ramps can get the stopping job done. If not, well . . . search YouTube for “runaway truck ramp,” and watch the “freak truck accident” video.

• Ramps vary in design, materials, construction, and effectiveness. For example, if the rig in this story’s intro had been going 60 mph, the ramp would have provided nearly 3000 retarding horsepower.

• States determine where ramps are constructed, based on such parameters as: runaway-truck accident rate at a candidate grade; length and percent of slope; traffic volume and percent of heavy-truck traffic; and conditions at the grade’s end, e.g., a sharp bend, a building, etc.

• “Runaway Trucks in Pennsylvania” (Carrier and Pachuta, SAE Technical Paper No. 811262) details the summer 1980 construction of a Pittsburgh-area ramp, which cost $600,000 (about $1.2 million in today’s dollars). Nearly 40 percent of that money went toward a retaining wall, which, depending on topography, is not always necessary.

• Upon driving a loaded dump truck onto the Pennsylvania ramp at 35 mph, the authors of the SAE study describe the stopping inertia as “strong but absent the jarring impact of other crashes.” Vehicle damage was confined to lower engine accessories and air tanks.

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