What Are Underride Guards and Why Do They Fail?

Tractor Trailer Underride Guard - Mansfield Bar

Underride guards, also known as Mansfield bars or rear impact guards, are crucial safety features attached to the rear and sides of large commercial vehicles like semi-trailers. Despite their importance, these safety devices often fail, leading to fatal accidents and severe injuries. This article delves into the history, function, issues, and potential improvements of underride guards.

What are Underride Guards?

Underride guards are steel barriers installed on the back and/or sides of large commercial trucks. These devices serve to prevent smaller vehicles from sliding beneath the truck in a collision, a phenomenon known as an underride crash. Underride crashes pose a significant risk due to the difference in height between passenger vehicles and large trucks, causing the passenger vehicle’s safety features to be bypassed and leading to severe, often fatal injuries for its occupants.

Historical Overview of Underride Guards

Underride guards have been part of the safety equipment on commercial trucks since the 1950s. In 1953, the U.S. National Transportation Safety Board (NTSB) introduced the first standards to prevent underride accidents, requiring vehicles with cargo beds 30 inches or more off the ground to have underride guards. However, these standards were limited and exempted many types of commercial vehicles.

The tragic death of Hollywood star Jayne Mansfield in an underride crash in 1967 prompted calls for improved underride guard standards. Despite these calls and subsequent studies highlighting the inadequacy of existing underride guard standards, progress has been slow due to opposition from the trucking industry and the failure of regulatory bodies to enforce stricter standards.

The Function of Underride Guards

In the event of a rear-end collision with a large commercial vehicle, an underride guard serves as a barrier that prevents the smaller vehicle from sliding underneath the truck. This is crucial because, in an underride crash, the larger vehicle’s trailer can intrude into the passenger compartment of the smaller vehicle, leading to severe injuries or fatalities.

Underride guards often fail due to being improperly installed, poorly designed or in bad condition. All of these factors can enhance risk and lead to catastrophic accidents. Even worse some commercial vehicles fail to operate with any guard at all. Though this is rare it does happen. An unmaintained truck is being operated negligently when driven for any reason without a guard installed.

Underride Guards: A Persistent Safety Issue

Despite their vital role in preventing underride crashes, underride guards are often poorly designed, inadequately maintained, and insufficiently regulated. Studies by the Insurance Institute for Highway Safety (IIHS) and other organizations have found that most underride guards fail to prevent underride in crashes involving only a small portion of the truck’s rear.

Moreover, the minimum strength and dimensions required for underride guards in the U.S. are inadequate, resulting in guards that often fail in crashes at speeds as low as 35 mph. Further complicating the issue is the fact that many types of commercial vehicles, such as dump trucks, are exempt from having any underride guards or rear collision bar.

Challenges in Implementing Effective Underride Guards

The implementation of effective underride guards or Mansfield bars faces several challenges. Firstly, the trucking industry has historically opposed stricter underride guard standards due to the associated costs. Secondly, the lack of a standard definition for underride crashes and inconsistency in data collection methods have hampered efforts to accurately assess the scale of the problem and develop effective solutions.

Towards More Effective Underride Guards

Despite these challenges, progress is being made towards more effective underride guards. For example, in 2022, the National Highway Traffic Safety Administration (NHTSA) issued a final rule requiring improved strength standards for Mansfield bars or rear underride guards.

Moreover, some truck manufacturers are already installing guards that are stronger than required by current standards. For instance, Canadian manufacturer Manac has developed an underride guard with vertical supports that are spaced closer to the edge of the trailer, providing greater protection against underride in crashes involving a small overlap with the trailer’s rear.

The Need for Continued Research and Regulation

While these developments are encouraging, continued research and regulation are needed to ensure the effectiveness of underride guards. This includes conducting additional research on side underride guards, developing standards for their implementation, and improving data collection methods for underride crashes.


What Can Victims Do in Underride Guard Failure Cases?

In injury cases where negligence exists on the part of any party such as a truck operator or a manufacturer, damages may be sought for improper actions or a failure to act with care. This must be proven and will require investigation and the collection of valid evidence. This process can be involved and usually requires the help of lawyers who have experience with these cases specifically.

If an underride accident victim can prove that the the injuries caused by faulty underride guards could have been prevented or mitigated, then a victim may file a lawsuit on the basis of a defective or dangerous product cause. There is no need to prove that any violations of federal law took place in cases brought to court with the cause being product liability. If a such an accident could have been avoided or had a better outcome due to an inexpensive or simple change to the guards on a truck that had a override guard that failed causing victims to be harmed, then a case may be built upon these grounds.

If you or a family member have suffered injuries due to a underride guard or any commercial vehicle accident it is in your best interest to consult with a qualified truck accident lawyer. The attorneys at Tate Law Offices have been helping trucking accident victims for more than 32 years. Our Texas commercial vehicle accident attorneys have a long history of proven success in cases that involve large trucks. Do not hesitate to contact us as soon as possible to being exploring your injury case.


Underride guards play a crucial role in preventing severe injuries and fatalities in collisions involving large commercial vehicles and smaller passenger vehicles. However, issues with their design, maintenance, and regulation mean that they often fail to fulfill their intended function. Ongoing research, stricter regulatory standards, and industry innovation are essential to enhancing the effectiveness of underride guards and reducing the incidence of underride crashes.