Underride Crashes: The Deadliest Type of Truck Accident

When a passenger vehicle slides under a commercial truck, the results are almost always catastrophic. Here is what you need to know about underride crashes and the ongoing fight for better safety standards.

What Is an Underride Crash?

An underride crash occurs when a passenger vehicle collides with a commercial truck and slides underneath the truck's body. Because the cargo area of a standard semi-trailer sits approximately four feet above the ground — well above the hood and windshield of most passenger vehicles — the structural crumple zones and safety features of the passenger vehicle are bypassed entirely.

The result is catastrophic. In a typical underride crash, the truck's trailer strikes the passenger vehicle at windshield height, causing devastating head and neck injuries that are frequently fatal. The Insurance Institute for Highway Safety (IIHS) has described underride crashes as "among the most deadly and preventable types of truck accidents."

Types of Underride Crashes

Rear Underride

Rear underride crashes occur when a passenger vehicle strikes the back of a commercial trailer. Federal regulations have required rear underride guards (also called "Mansfield bars," named after actress Jayne Mansfield who died in a 1967 rear underride crash) on commercial trailers since 1953. However, current federal standards for rear underride guards are widely considered inadequate.

IIHS testing has found that many trailers equipped with federally compliant rear guards fail to prevent underride in offset crashes — where the vehicle strikes the corner of the trailer rather than the center. In IIHS testing, even trailers with the most robust rear guards available failed to prevent underride in 30% and 50% offset crash scenarios.

Side Underride

Side underride crashes occur when a passenger vehicle strikes the side of a commercial trailer. Unlike rear underride, there is no federal requirement for side underride guards on commercial trailers. Side underride crashes are particularly common at intersections, where a truck making a wide turn may swing across multiple lanes of traffic.

IIHS research has found that side underride guards could prevent or reduce the severity of injuries in a significant percentage of fatal side-impact truck crashes. Despite this evidence, the trucking industry has successfully resisted mandatory side underride guard requirements for decades.

Front Underride

Front underride crashes, in which a vehicle slides under the front of a truck, are less common but can occur when a truck rear-ends a passenger vehicle at high speed. The height of the truck's front bumper relative to the passenger vehicle's roof can cause the same catastrophic structural bypass as rear and side underride crashes.

The Regulatory History

The history of underride guard regulation in the United States is a story of incremental progress against sustained industry resistance.

1953: FHWA first requires rear underride guards on commercial trailers.

1967: Actress Jayne Mansfield dies in a rear underride crash on a Louisiana highway. The incident generates public attention but no immediate regulatory change.

1996: NHTSA updates rear underride guard standards, requiring guards to withstand 50,000 pounds of force. However, the standard does not address offset crashes.

2011: IIHS publishes research showing that current rear underride guard standards are inadequate for offset crashes.

2015: The STOP-Underrides Act is introduced in Congress, requiring side and front underride guards and stronger rear guards. The bill has been reintroduced multiple times but has never passed.

2022: NHTSA proposes updated rear underride guard standards that would require guards to withstand offset crash forces. The rule has not been finalized.

The Human Cost

IIHS data suggests that improved underride guard standards could prevent hundreds of deaths annually. The organization estimates that approximately 400 people die in rear underride crashes each year, and that a significant percentage of these deaths could be prevented by guards that perform adequately in offset crash scenarios.

Side underride crashes are estimated to kill an additional 200-300 people annually, with many more suffering serious injuries.

Legal Implications for Victims

Underride crash cases present unique legal challenges and opportunities:

Equipment defect claims: When a crash occurs because an underride guard failed to perform as designed, the truck manufacturer, trailer manufacturer, or guard manufacturer may be liable for a defective product.

Regulatory violation claims: When a truck is not equipped with a required rear underride guard, or when the guard does not meet federal standards, the carrier may be liable for a regulatory violation.

Negligent design claims: Some plaintiffs have successfully argued that the design of commercial trailers — which creates the underride hazard in the first place — constitutes a defective design that the manufacturer should have remedied.

Advocacy and Reform

Several organizations are actively working to improve underride guard standards:

The Truck Safety Coalition has been advocating for stronger underride guard requirements since the 1990s, often led by families of underride crash victims.

The Insurance Institute for Highway Safety conducts ongoing crash testing of underride guards and publishes research supporting stronger standards.

Citizens for Reliable and Safe Highways (CRASH) was founded by Cathy Bernstein after her daughter was killed in an underride crash and has been a leading voice for regulatory reform.

Frequently Asked Questions

Are underride guards required on all commercial trucks? Rear underride guards are required on most commercial trailers, but the current federal standards are widely considered inadequate. Side underride guards are not federally required, though some carriers voluntarily install them.

What is a "Mansfield bar"? A Mansfield bar is a colloquial term for a rear underride guard, named after actress Jayne Mansfield who died in a rear underride crash in 1967. The term is sometimes used to refer to any rear underride guard.

Can I sue a truck manufacturer for an underride crash? Potentially, yes. If the underride guard failed to perform as designed, or if the trailer design created an unreasonable underride hazard, the manufacturer may be liable. These cases require specialized engineering expertise and an attorney experienced in product liability litigation.