The National Highway Traffic Safety Administration intends to implement additional requirements that auto safety groups argue do not go far enough.

By Arthur F. Foerster and De Vann S. Sago

On July 15, 2022, the National Highway Traffic Safety Administration (NHTSA) issued a Final Rule effective January 2023 that requires additional protection in rear underride protection on trailers and semi-trailers.[1]

Rear underride crashes typically occur when a passenger vehicle collides into the rear end of a large trailer or semi-trailer, and the front end of the passenger vehicle “underrides” (i.e., slides under) the trailer.[2] Underride occurs because the trailer sits higher than the front of the passenger vehicle.[3] In extreme cases, a passenger vehicle underrides the trailer to the point that the trailer hits and/or enters the passenger compartment of the colliding vehicle.[4] Known as “Passenger Compartment Intrusion” or “PCI,” these crashes can result in severe injury or death.[5] Rear impact guards are designed to absorb energy and prevent the passenger vehicle from sliding too far under the trailer.[6] Under the Final Rule, NHTSA is requiring additional protection in underride crashes in which: (1) a passenger vehicle hits the center of the rear of a trailer or semi-trailer; and (2) 50% of the width of a passenger vehicle overlaps the rear of a trailer or semi-trailer.[7]

Current Requirements

Federal Motor Vehicle Standards (FMVSS) Nos. 223 and 224 were first issued in 1996.[8] FMVSS No. 223, “Rear impact guards,” is an equipment standard that specifies strength and energy absorption requirements.[9] FMVSS No. 224, “Rear impact protection,” is a vehicle standard that requires that new trailers and semi-trailers with a gross vehicle weight rating (GVWR) of at least 10,000 pounds be equipped with rear impact guards meeting FMVSS No. 223.[10] Together, FMVSS Nos. 223 and 224 ensure that rear impact guards: 1) are configured low and wide to impede a striking passenger vehicle; 2) are strong enough to withstand a 30 mph impact of a colliding passenger vehicle; and 3) have energy-absorbing capability to further mitigate harm to occupants in a striking passenger vehicle.[11]

IIJA’s Mandate to Upgrade FMVSS Nos. 223 and 224

Congress passed the Biden Administration’s Infrastructure Investment and Jobs Act (IIJA) in November 2021.[12] Among the law’s many other mandates, Section 23011(b)(1)(A) of IIJA directs that within one year of the law’s enactment, the Secretary of Transportation (NHTSA by delegation) shall promulgate regulations that upgrade rear impact guards and revise FMVSS Nos. 223 and 224.[13] More specifically, IIJA provides that the regulations shall require new trailers and semi-trailers to be equipped with rear impact guards designed to prevent PCI from a trailer or semi-trailer when a passenger vehicle traveling at 35 mph makes an impact:

  1. with the center of the rear of the trailer or semi-trailer;
  2. in which 50% of the width of the passenger vehicle overlaps the rear of the trailer or semi-trailer; and
  3. in which 30% of the width of the passenger vehicle overlaps the rear of the trailer or semi-trailer.[14]

Although IIJA mandated both the center of the rear and 50%-overlap standards, the 30%-overlap standard was required only if the Secretary determined that a revision to address such an impact would otherwise meet the requirements of the Safety Act, 49 U.S.C. §§ 30111(a), (b). These requirements authorize the Secretary to issue safety standards that are reasonable, practicable, and appropriate for the types of vehicles for which the standard is prescribed.[15] After analyzing the issue of a 30%-overlap crash, NHTSA determined that the available data did not show such a standard would be reasonable, practicable, and appropriate for all the trailers subject to the standard.[16]

Additionally, Section 23011(b)(2) of IIJA directs the Secretary to conduct further research on the development of rear impact guards that can protect passengers at speeds up to 65 mph and, if warranted, update the standards accordingly.[17] IIJA also directs the Secretary to perform research on side underride guards, within one year, and to assess the feasibility, benefits, and costs of such guards on new trailers and semi-trailers, and, if appropriate, to develop standards.[18] NHTSA discussed many of these IIJA requirements in the Final Rule. For instance, NHTSA will establish a federal advisory committee on underride protection.[19] This committee will research side underride guards for trailers and semi-trailers to assess their effectiveness, feasibility, benefits, costs, and impact on intermodal operations.[20] NHTSA also plans to publish an advance notice of proposed rulemaking to consider requirements for side underride guards for crashes into the sides of trailers and semi-trailers.[21] NHTSA will also improve data collection of underride crashes by recommending inclusion of underride data in state crash data systems and by educating state and local police departments on identifying and recording underride crashes.[22] Finally, NHTSA will conduct research on rear impact guard designs that better protect occupants of passenger vehicles in additional rear underride crash scenarios.[23]

NHTSA Accused of Not Going Far Enough

On August 25, 2022, several safety groups petitioned NHTSA to reconsider the Final Rule.[24] Petitioners allege that the Final Rule failed to consider all relevant available data and testing on underride crashes, including with respect to dropping the 30%-overlap crash requirements.[25] Petitioners request a stay of the effective date of the Final Rule while their petition is being considered, calling the Final Rule “inadequate and dangerous…”[26] NHTSA itself estimates in the Final Rule that 94% of new trailers sold in the US already are designed to comply with the new standards.[27] NHTSA used this figure to justify the relatively low cost for the new standard.[28] Petitioners, however, allege that this percentage proves NHTSA did not go far enough and that this level of pre-existing compliance indicates that the Final Rule “scarcely achiev[es] measurable progress in underride safety.”[29] NHTSA also estimates that 28% of new trailers sold in the US already are designed to comply with the 30%-overlap standard.[30] Petitioners cite this figure in arguing that “[s]etting an unreasonably low standard for underride safety will diminish market demand for strong underride guards as compliance can now be achieved with substandard guards.”[31]


NHTSA’s policy is to issue notice of the action taken on a petition for reconsideration within 90 days after the closing date for receipt of such petitions, unless it is found impracticable to take action within that time.[32] How NHTSA will respond to the recent petition to reconsider, or whether the additional research mandated by IIJA will support increased requirements, remains to be seen.

Latham & Watkins will continue to monitor developments in this area.



[1] Federal Motor Vehicle Safety Standards; Rear Impact Guards, Rear Impact Protection, 87 FR 42339 (July 15, 2022) (to be codified at 49 CFR 571).

[2] Id. at 42340.

[3] Id.

[4] Id.

[5] Id.

[6] Id. at 42342, 42358. Typically, the vertical members of the rear impact guard are attached to the longitudinal frame rails so that impact loads are directly transmitted to the frame rails. Id. at 42342.

[7] Id. 42339.

[8] Id. at 42351.

[9] Id. at 42340.

[10] Id.

[11] Id.

[12] Id. at 42341.

[13] Id.

[14] Id.

[15] Id. at 42341-42.

[16] Id. at 42342-43.

[17] Id. at 42341.

[18] Id.

[19]; 87 FR at 42341, 42344.

[20]; 87 FR at 42341, 42344.

[21]; 87 FR at 42341, 42344.

[22]; 87 FR at 42341-42, 42344.

[23]; 87 FR at 42341, 42343-44, 42350.

[24] Petition for Reconsideration of the Final Rule on Federal Motor Vehicle Safety Standards; Rear Impact Guards, Rear Impact Protection Published at 87 Federal Register 42339, July 15, 2022, Docket NHTSA-2022-0053 (August 25, 2022);

[25] Petition for Reconsideration at 2-4.

[26] Petition for Reconsideration at 5.

[27] 87 FR at 42343-44.

[28] Id.

[29] Petition for Reconsideration at 5.

[30] 87 FR at 42359-60.

[31] Petition for Reconsideration at 5.

[32] 49 CFR Pt. 553, App. A.