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What tractor trailer crash tests reveal about side underride guards

By Rohan L. Lewis July 5, 2017
underride guards photo 1
In this side underride guard test, the guard bent but didn’t allow the car to go underneath the trailer, letting the car’s airbags and safety belt properly restrain the test dummy in the driver’s seat.

Auto insurers have a vested interest in the safety of vehicles they insure, and recent findings from an Insurance Institute for Highway Safety (IIHS) study on tractor trailers affect both commercial and personal insureds. IIHS conducted tests that show strong side underride guards on tractor trailers are effective for preventing underride crashes.

Vehicle underride, side underride crashes studied

Underride guards are steel bars attached below a trailer to prevent a smaller vehicle from going under the trailer during a crash. The industry knows that rear underride guards are effective in preventing vehicle underride, and the latest IIHS tests further illustrate the importance of countermeasures to prevent side underride crashes, too.

This is an important issue: Statistics show that in 2015, of the 1,542 passenger-vehicle occupants killed in two-vehicle crashes with a tractor trailer, 301 died when their vehicles struck the trailer’s side. Because of gaps in federal crash data, IIHS researchers can’t determine exactly how many of those crashes involved underride, but they estimate it occurs in about half of all fatal crashes involving large trucks and passenger vehicles.

IIHS performed the tests in the spring of 2017, marking the first time IIHS has evaluated a side underride guard. The Institute ran two 35-mph crash tests: one with a side underride protection device and one with a fiberglass side skirt intended to improve aerodynamics, not underrides. The results were dramatically different.

underride guards photo 1
In this second test with the aerodynamic device, the car ran into the trailer and kept going. The impact sheared off most of the car’s roof, and the vehicle became wedged beneath the trailer. In the real world, this crash would likely be fatal.

Dramatic test results

In both tests, a midsize car struck the center of a 53-foot-long dry van trailer. In the side underride guard test, the guard bent but didn’t allow the car to go underneath the trailer, letting the car’s airbags and safety belt properly restrain the test dummy in the driver’s seat. In the second test with the aerodynamic device, the car ran into the trailer and kept going. The impact sheared off most of the car’s roof, and the vehicle became wedged beneath the trailer. In a real-world crash like this, the car’s occupants would probably have sustained fatal injuries and the trailer significant damage.

The test adds to the body of evidence from a 2012 IIHS study that found strong side underride guards can potentially reduce injury risk in about three-fourths of large-truck side crashes that produce a fatality or serious injury to a passenger vehicle occupant. The proportion increased to almost 90 percent when restricted to crashes with semitrailers.

Side underride guards not federally mandated

Federal law requires large trucks to have rear underride guards but not side underride guards. At least three U.S. cities—Boston, New York, and Seattle—mandate side guards on city-owned and/or contracted trucks as part of Vision Zero initiatives to eliminate crash deaths and injuries. The trucking industry has concerns about installing side underride devices due to the added weight, which reduces the amount of cargo that can be transported. It prefers automated equipment that prevents a vehicle from striking the side of the trailer, but that will take many years before all vehicles can be so equipped. To properly determine risk and underwrite commercial policies, commercial auto insurers need to know whether their insureds use underride guards.

A copy of the IIHS release is available here. Verisk's Engineering and Safety Service (E&S™) works with our commercial auto team to keep customers informed on these and many other issues related to loss control. For information on Verisk’s Commercial Auto Solutions, visit our website.


Rohan L. Lewis is a product manager for Verisk Insurance Solutions–Commercial Lines Underwriting. You can contact Rohan at rlewis@verisk.com.