While long-haul truckers and other fleet operators must deal with underride requirements and when to install guards, ready-mix trucks and precast producers operating flat-bed vehicles also should be aware of this issue.

Rules for rear impact protection, commonly known as an ICC bumper, are included in 49 Code of Federal Regulations (CFR) 393.86. The directives, which are part of the Federal Motor Carrier Safety Regulations (FMCSR), apply to trucks meeting the definition of a commercial motor vehicle. The Federal Motor Carrier Safety Administration oversees these requirements. While not all trucks fall under their authority, most states have adopted them for intrastate commerce.

For trailers and semi-trailers with a gross vehicle weight rating (GVWR) of 10,000 pounds 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).

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 FMCSR, so the timeline dictating which set of mandates applies to a given vehicle can be confusing.

Another common misunderstanding involves similar differences, such as guard positioning. For those trucks, under the FMCSR, 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 FMVSS, it must be no more than 22 inches above the ground and within 1 foot of the rear extremity.

Also, 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 FMCSR 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.