(WHTM) — You may have seen them driving through mountainous terrain. A sign that says “Runaway Truck Ramp” and a long road going up the side of a hill or a mountain, or a plot of sand.

These are called runaway truck ramps. But, how do they work? How does it bring a huge truck that can weigh up to around 80,000 pounds to a dead stop?

What is a Runaway Truck Ramp?

By definition, runaway truck escape ramps are designed to be emergency locations that use sand, gravel, or wire nets to slow down a large vehicle quickly in the event of a brake failure.

Most of these ramps make use of arrester beds, which are large areas of sand, or gravel. These materials are selected because when a wheel of a large vehicle hits the sand or gravel, the material in the area moves away from each other, allowing the truck to sink into the gaps.

Business Insider states that these runaway truck ramps are shallow when first entered, but can reach a depth of 48 inches once a truck travels 100 feet into the ramp. When a truck enters the area, it has little resistance at first and that causes the vehicle to gradually reduce in speed. This is to lessen injury to the driver and gives the truck less chance of tipping over.

Types of Runaway Truck Ramps

There are three basic designs of escape ramps: The sandpile bed, the gravity escape ramp, and the mechanical arrester ramp.

The sandpile bed contains loose rows of sand, perpendicular to the direction of travel. So, when the truck collides with the pile, the energy from the truck is then transferred to the sand. This can be rather jarring for the driver and can cause injury, so the gravity escape ramp was invented.

These ramps are angled up the side of a mountain or hill. Business Insider said that a 10% grade can allow a truck to stop up to 85 feet sooner. Gravity ramps are the most cost-effective where natural rises occur adjacent to the road. But in cases where that’s not possible, state agencies turned to a more unique way of slowing runaway trucks.

The mechanical arrester ramp can be installed on flat surfaces and even can be installed on downward slopes. This design does not feature an arrester bed, but rather a series of stainless steel catch nets. The nets absorb the energy from the truck, and like a rubber band being pulled, the force exerted on the truck increases the further it travels.

The downside to these ramps is that they are a one-way trip. Usually, the truck cannot be driven and will need to be towed, and the ramp would need to be reset.

So, what do you do if you need to use a runaway truck ramp?

Many hope to never use one of these ramps. But, Encore Protection has given some advice on how to use one of these ramps.

  1. Remain Calm
    • It may be hard to do as you fly downhill with no breaks. But, the key is to maintain composure and be aware of your surroundings.
  2. Engage the Jake Brake
    • This will prevent uncontrollable speeds and also make it somewhat manageable to move around slower traffic.
  3. Locate the Ramp and Center the Vehicle
    • Locate the truck escape ramp and center your truck as best as you can. Once you hit the sand or gravel incline, you will need to keep the wheel as steady as possible.
  4. Assess the situation and move to safety
    • If you are not injured, turn the vehicle off and call emergency services and wait in a safe location