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How Crash Cushions Make Highways Safer

Highway administrators and engineers have learned in recent decades how to reduce the impact of vehicle collisions with crash cushions. Whether it's cars, trucks or motorcycles crashing into these fixed cushions known as impact attenuators, the strategy is saving lives. One of the most useful applications for these objects is to protect road crews.

Accident Research Leads to Safer Conditions

The National Cooperative Highway Research Program Report was published in 1975 for engineers as well as federal and state highway officials. The report recommended the adoption of gathering waste materials such as scrap tires to fill up rigid immovable objects serving as crash cushions. This report confirmed that an earlier 1972 Federal Highway Administration (FHA) memorandum was correct that crash cushions provide sufficient impact attenuation to reduce accidents and injuries caused by vehicles crashing into fixed objects.

One of the suggestions in the report for highway officials was that attenuators should not be used where vehicles crashing into them could be returned to the traffic stream. The report proposed the frontal area of the cushion should use softer material than the rest of the design materials to lessen the impact of light vehicles.

What's Inside Crash Cushions

Crash cushions reduce kinetic energy, in which some models convert it to heat through a tube. The key is to use crushable materials that absorb energy, so that upon impact the vehicle bounces off the cushion. Kinetic energy from a crash can be reduced by using soft materials such as sand-filled barrels, hollow steel cylinders or other lightweight crushable materials. The original concept of crash cushions was introduced by the Goodyear Tire and Rubber Company.

At the time, 200 million scrap tires accumulated each year in the United States. Only 10 percent of these scraps were recycled, which still left about 180 million tires piling up in landfills and junkyards. Goodyear was looking for an efficient disposal method for these scraps and was the first to envision them for manufacturing low cost crash cushions as highway safety features. The company worked with the University of Cincinnati to conduct the initial tests, which involved analyzing high speed photography taken of crash test dummies in cars crashing into cushions at speeds up to 80 mph.

Early tests for these cushions included stacks of rubber tires full of sand on round cardboard cartons. The cartons were positioned at the location where impact occurs. Other designs included the use of tires filled with empty beverage cans, fiberized aluminum and used consumer containers. Today after many further studies, cushions are barrels that commonly consist of sand or water.

What Happens Upon Impact

Crash pads are placed in strategic positions, such as where highways divide and at off-ramps. These places are where many serious accidents occur due to drivers changing their minds at the last minute. The crash pads can protect drivers and passengers moving up to 70 mph before impact.

When a vehicle runs into a crash cushion, the attenuator crushes into itself without the inner materials being destroyed. The parts within the attenuator can be used repeatedly, whether the attentuator is meant to be permanent or temporary. Either way, the cushions can be restored to their normal forms in about ten minutes. Portable attentuators are usually pre-assembled to save setup time where they will be used. Road crews often use multiple attentuators that can be quickly installed.

Conclusion

Using crash cushions on freeways, particularly where road work activity occurs, has been proven to reduce traffic fatalities and injuries. For more information about products designed to make highways safer, call Zumar at our Arizona, California or Washington location.