A Mansfield bar is the horizontal guard below the rear of a truck trailer. Its formal name is a rear impact guard or rear underride guard. It is intended to limit how far a smaller vehicle can slide beneath the trailer when it strikes from behind.
The bar is only part of the protection. Its supports, connections, and the trailer structure that carries the load also matter. After an underride collision, finding a bar on the trailer does not answer whether it was properly installed, maintained, or able to engage the car in that particular impact.
What an underride guard can and cannot do
A passenger car’s front end is lower than the body of many trailers. In an underride crash, the car can travel beneath that body, allowing the trailer to intrude into the passenger compartment. A rear guard is designed to limit that movement. It does not promise protection at every speed, angle, or point of contact, and a rear bar does not protect a car striking the trailer’s side.
NHTSA’s 2022 rear-impact rule strengthened the federal requirements for newly manufactured trailers and semitrailers. It addressed rear impacts at 35 mph involving the center of the trailer and crashes with 50 percent overlap of the passenger vehicle. The rule took effect January 11, 2023, with a July 15, 2024 compliance date.
Those test conditions matter. An angled impact near a trailer’s corner is not the same event as a centered test. Neither a damaged guard nor serious intrusion, standing alone, proves that the guard violated the applicable standard. The inspection must establish what failed, how the vehicles met, and whether a defect or inadequate maintenance contributed to the injuries.
Which trucks must have a rear guard?
The answer depends on the vehicle’s type, manufacture date, weight rating, configuration, and any applicable exception. Do not apply one trailer measurement to every box truck, older vehicle, or specialized trailer.
For covered trailers and semitrailers manufactured on or after January 26, 1998 with a gross vehicle weight rating of at least 10,000 pounds, 49 C.F.R. section 393.86(a) refers to the federal guard and installation standards in effect when the vehicle was manufactured. It lists exceptions, including certain low-chassis, wheels-back, and special-purpose vehicles. Section 393.86(b) contains a different rear-protection rule for other covered vehicles.
Scroll horizontally to see all columns. Use the arrow keys when the table is focused.
| Rule | What it addresses | What to establish after a crash |
|---|---|---|
| 49 C.F.R. 393.86 | Rear guards and rear-end protection on covered commercial vehicles | The vehicle category, date, configuration, applicable standard, and any claimed exception |
| FMVSS 223 | The guard’s strength, energy absorption, labeling, and installation instructions | The guard’s identity, design, attachment hardware, and relevant performance requirements |
| FMVSS 224 | Installation and positioning of guards on covered trailers and semitrailers | How the guard was mounted and whether its position matched the applicable requirements |
FMVSS 224 specifies a maximum guard height of 560 millimeters, approximately 22 inches, with qualifications including rounded corners. It also specifies the vehicle condition used for measurement: level ground, unloaded, and properly configured tires and suspension. A photograph of a damaged, loaded trailer sitting at an angle in a ditch is not a reliable substitute for that measurement.
The trailer should be examined along with the car
The guard’s post-crash condition needs context. A torn connection may reflect crash loading, an earlier poor repair, corrosion, or some combination. Before deciding what it means, document the bar, supports, welds, bolts, trailer frame, impact marks, and passenger-compartment damage. Preserve detached pieces as well as the equipment still attached to the trailer.
Identify the tractor and trailer separately using their vehicle identification numbers, plates, and unit numbers. A company name on the tractor does not establish who manufactured, owned, leased, or last repaired the trailer. Those records help determine which businesses may hold the evidence and which work each performed.
Pre-crash inspection photographs and repair records can show whether the guard had been damaged or modified before the collision. A report for the tractor is not necessarily a report for the trailer’s rear guard.
Video and electronic records may help establish speed, braking, the trailer’s movement, and the angle of contact. The available information varies by system.
Who caused the collision, and what caused the injuries?
These questions can overlap without being identical. Driver conduct may explain why two vehicles collided. A guard’s design, installation, or condition may raise a separate question about the resulting intrusion and injury. An investigation should test both rather than assume that a rear-end collision resolves every potential claim.
Under Louisiana Civil Code article 2315, fault must be connected to the damage claimed. A driver, carrier, trailer owner, or repair company is not responsible simply because it appears in the equipment’s paperwork. The claim must identify the relevant conduct or responsibility and explain how it contributed to the harm.
A claim against a manufacturer requires a separate products-liability analysis. R.S. 9:2800.54 requires proof of an unreasonably dangerous product characteristic, causation, and damage arising from a reasonably anticipated use. It identifies construction or composition, design, inadequate warning, and failure to conform to an express warranty as the statutory categories. The condition of the product when it left the manufacturer’s control, and any later alteration, can therefore be important.
For injury-causing conduct on or after January 1, 2026, Civil Code article 2323 generally bars recovery when the injured person’s negligence reaches 51 percent. Below 51 percent, damages are reduced proportionately. Earlier events require application of the prior fault rule. A possible guard claim does not erase evidence of the passenger driver’s conduct, and that conduct does not eliminate the need to examine the guard.
What to do while the vehicles are still available
Emergency care comes first. Once it is safe to address the claim, keep photographs, video, witness information, the crash report number, and tow or storage documents. Do not climb beneath an unstable trailer or enter traffic to inspect a guard yourself.
Promptly identify where both vehicles and any detached parts are being held. A lawyer can request preservation and arrange an appropriate inspection before the trailer returns to service or the car is repaired or salvaged. The request should identify the actual equipment and relevant records. It does not establish that every requested item exists, and it does not replace an inspection agreement or formal discovery when those are needed.
Most Louisiana delictual claims arising on or after July 1, 2024 fall under the two-year period in Civil Code article 3493.1; older claims generally remain subject to the former one-year rule. Exceptions, fatal claims, and government defendants require separate attention. Do not use that filing period as a reason to postpone an equipment inspection.
Our truck accident lawyers can review the photographs and records, identify the trailer and companies involved, and assess whether a guard inspection is needed. Call (225) 500-5000 or use the contact form below.
Sources checked: September 29, 2026. Last reviewed: September 28, 2026.