Have you ever searched the Internet for videos of trucks using a runaway-truck ramp? If so, you might have seen this video:

A truck having to use a runaway truck ramp is a frightening thing to see. But truck ramps are very effective at stopping trucks that have lost use of their brakes. There are two types of runaway truck ramps:

1. Gravity ramps: A truck takes the ramp and experiences an uphill grade that naturally will stop it.
2. Gravel arrester beds: These are on a flat-level grade. Trucks taking the ramp will run into a bed full of small, round gravel. The friction from the wheels going through the gravel is what slows the truck and eventually stops it.

Why are they necessary? Here's a quick answer from ADOT’s Roadway Design Guidelines:

The combination of heavy trucks and steep highway downgrades presents a potential safety hazard... Defective or incorrectly adjusted braking systems on trucks or trailer, among other things, can contribute to brake overheating and failure resulting in the driver's inability to control vehicle speeds on downgrades. Truck escape ramps offer an opportunity for out-of-control trucks to exit the highway and come to a controlled stop.

For more details on runaway truck ramps, click here.