Rear impact guard requirements

This article was published in the September 2015 edition of NTEA News

Question: We are a truck equipment distributor receiving numerous customer calls on rear underride requirements. There seems to be some confusion as to when guards must be installed. Can you help clarify?

Answer: Your customers’ uncertainty is common. There are two similar requirements resulting in visually identical features. They are intended to reduce injuries and fatalities associated with lighter vehicles by preventing intrusion underneath the rear of a heavier vehicle during an impact, as well as absorbing some of the collision’s energy. One set of mandates applies to trucks, while the other is specific to trailers.

For straight trucks, longstanding rules for rear impact protection (commonly known as an ICC bumper) are contained in 49 Code of Federal Regulations (CFR) 393.86 (see Figure 1).

These directives, which are part of the Federal Motor Carrier Safety Regulations (FMCSRs), apply to trucks meeting the definition of a commercial motor vehicle (see definition from 49 CFR Part 390.5 below). The Federal Motor Carrier Safety Administration (FMCSA) is the agency overseeing these requirements. While not all trucks fall under their authority, most states have adopted them for operations in intrastate commerce, so your customers and the general public are best served by providing features to comply with these same rear impact protection guidelines.

For “trailers and semitrailers with a gross vehicle weight rating (GVWR) of 4,536 kg
or more”, rear impact guards are required under Federal Motor Vehicle Safety Standard (FMVSS) 224, which is governed by the National Highway Traffic Safety Administration (NHTSA) (see Figure 2).  

After FMVSS 224 took effect in 1998, new trailers with a GVWR of 10,000 pounds or more have had to comply with this standard (apart from those meeting certain exclusions). However, trailers were previously subject to the same requirements as straight trucks under the FMCSRs, so the timeline dictating which set of mandates applies to a given vehicle can be confusing to
end users.

Another common misunderstanding involves similar differences, such as guard positioning. For trucks, under the FMCSRs, the structure used to meet the regulations must reside within 30 inches of the ground and 2 feet of the rear extremity when the vehicle is unloaded. For trailers under the FMVSSs, it must be no more than 22 inches above the ground and within 1 foot of the rear extremity.

In addition, the structure used to meet FMVSS 224 can look identical to the same horizontal beam with two vertical supports commonly used to meet FMCSA rules on straight trucks. But the structure used for trailers has performance requirements from FMVSS 223, whereas FMCSRs do not have test regulations. This is often another source of uncertainty, where the seemingly identical structure does not have the same, more stringent directives when attached to a straight truck as when attached to a trailer — even with the same GVWR.

Compounding the similar differences, performance requirements for rear impact guards on trailers in Canada — contained in Canadian Motor Vehicle Safety Standard (CMVSS) 223 — were upgraded in 2007 to necessitate more energy absorption and reduce intrusion. Although they may look identical, a guard on a U.S. trailer is not accepted on the same trailer imported into Canada unless it meets the higher performance criteria of CMVSS 223.

Efforts are being made to harmonize these requirements. The U.S. and Canada are working to unify the respective rules of each country across a number of industries — including automotive safety — and trailer rear impact guards are on the list of standards to be made equivalent. Also, NHTSA recently published an advance notice of proposed rulemaking in an effort to synchronize truck and trailer rear underride protection in the U.S.


From 49 CFR Part 390.5
Commercial motor vehicle means any self-propelled or towed motor vehicle used on a highway in interstate commerce to transport passengers or property when the vehicle—

  • Has a gross vehicle weight rating or gross combination weight rating, or gross vehicle weight or gross combination weight, of 4,536 kg (10,001 pounds) or more, whichever is greater; or
  • Is designed or used to transport more than 8 passengers (including the driver) for compensation; or
  • Is designed or used to transport more than 15 passengers, including the driver, and is not used to transport passengers for compensation; or
  • Is used in transporting material found by the Secretary of Transportation to be hazardous under 49 U.S.C. 5103 and transported in a quantity requiring placarding under regulations prescribed by the Secretary under 49 CFR, subtitle B, chapter I, subchapter C.”


Interstate commerce means trade, traffic, or transportation in the United States—

  • Between a place in a State and a place outside of such State (including a place outside of the United States);
  • Between two places in a State through another State or a place outside of the United States; or
  • Between two places in a State as part of trade, traffic, or transportation originating or terminating outside the State or the United States.”


Intrastate commerce means any trade, traffic, or transportation in any State which is not described in the term ‘interstate commerce.’”