Runaway Truck Ramps

Contributor: Jay Gregorio. Lesson ID: 13307

Have you ever been driving on the highway and seen a road leading to nowhere? Why is it there? What does it do? What does science have to do with it? Speed into this lesson to find out!


Physical Science, Physics

learning style
Auditory, Visual
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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  • Are there roads created with the hope that no one will use them?

If you ever drive along a steep road on the side of a mountain, you will see one of the most useful - but hopefully not used - roads, called a runaway ramp!

runaway ramp

Runaway ramps are an important, but often unknown, road safety feature designed to prevent accidents.


Large trucks like the one pictured above are called tractor-trailers, semis, or even 18-wheelers because they have 18 wheels. These trucks, which weigh about 35,000 pounds themselves, can carry up to 45,000 additional pounds in cargo.

That means each truck could weigh up to 80,000 pounds!

The laws of physics explain that a massive object like that truck moves very fast and is, therefore, harder to stop. The momentum of the truck is so large that the damage it would cause by hitting something on the road if its brakes failed would be catastrophic.

In this lesson, you will explore the science behind truck runaway ramps and see how useful they are in avoiding fatal accidents on the road involving these massive machines on wheels!

Truck brakes are designed to withstand the normal amount of pressure created when they are used to slow down or stop the truck.

On a straight and level road, stopping frequently may not even be necessary because the truck can cruise at an almost constant speed with no issue.

Problems can arise, however, when the road has a continuous and steep decline that requires the truck to slow down.

  • So, what would a cautious driver do?

Press on the brakes slightly to slow it down.

trucks driving down a steep, curved road

While this generally works, there are situations when pressing on the brakes while moving downhill creates too much pressure on the brakes, causing them to fail. If that happens, the only way to stop the speeding truck is to make it more difficult to continue its motion - like driving up a rocky road!

This is where runaway truck ramps, sometimes called escape ramps, become a necessity.

The Purpose of the Ramp

Runaway truck ramps are placed on major roadways, particularly those with steep declines, to help stop large trucks that are unable to stop on their own using their brakes.

The objective is to slow down the truck and stop it gradually while keeping everyone safe, including the driver.

Newton's first law of motion states that an object in motion will continue moving unless acted upon by an external force. This external force does not necessarily need to be an applied force, like the brakes.

This means that the road can be redesigned to slow down the truck.

Factors That Determine Where to Build Ramps

Road safety is a primary concern for highway engineers. These roads are designed to provide maximum safety both for drivers and pedestrians.

Building a runaway truck ramp in a particular location is based on the following considerations:

  • the length and percent of the road's grade or slope
  • the road conditions at the end of the grade
  • the average daily truck volume and percent of truck traffic on the road
  • the number of vehicular accidents involving trucks on the road

Design of the Runaway Truck Ramp

Gravity is the usual cause of brake failure on those long and steep road declines. Therefore, the design of the ramp should go against gravitational forces.

Moving uphill negates the attractive force of the earth, thus slowing down the truck. Adding elements that create friction will also slow down the truck's movement.

There are four basic types of runaway truck ramps:

Gravity Escape Ramp

gravity escape ramp in Colorado, USA

Image by Quentin Scouflaire, via Wikimedia Commons, is licensed under the CC BY 2.0 license.

The natural slope of a surrounding mountainside provides the perfect uphill ramp for a truck to slow down and stop. The surface of the ramp consists of gravel that increases the friction between the tires and the road.

Sand Pile Ramp

sand pile ramp in North Carolina, USA

Image by Billy Hathorn, via Wikimedia Commons, is licensed under the CC BY-SA 3.0 license.

When the slope of the road is less, a series of sand piles are placed on short ramps to help stop the truck.

Arrester Bed Ramp

arrester bed ramp in Perth, Western Australia

Image by JarrahTree, via Wikimedia Commons, is licensed under the CC BY 2.5 AU license.

This is a short ramp covered with gravel used on minimal grade or less steep slopes.

Mechanical-Arrester Ramp

mechanical-arrester ramp in Connecticut, USA

Image by Hanleyrc, via Wikimedia Commons, is licensed under the CC BY-SA 3.0 license.

This short ramp has stainless-steel nets stretched across its beginning and often has a barrier at the end.

Watch How Truck Escape Ramps Stop Out-Of-Control Big Wheelers, from Business Insider, to see how they work:

Image - Video

Runaway truck ramps are one of the most practical yet ingenious ways of keeping safety a priority on the road. But as always, it comes with a cost. Truck drivers, who use an escape ramp, then have to pay to rescue their truck.

Watch What happens when a driver is forced to use a runaway truck ramp? from 9NEWS in Colorado:

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While paying to have your truck towed or fixed is no fun, there is nothing scarier than an out-of-control truck that is unable to stop!

Thank goodness for runaway truck ramps. While you may not live in a mountainous area or be a driver anytime soon, it is still important to understand all road safety features.

Driving is a privilege, and all drivers are responsible for making sure their vehicles are in good condition and that their driving is safe.

In the Got It? section, complete some activities that test your knowledge about this engineering design!

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