The NPRM is intended to work toward implementing the DOT strategy by requiring heavy vehicles (vehicles with a GVWR greater than 10,000 pounds) to have AEB and ESC systems to mitigate the frequency and severity of rear-end collisions with vehicles.  In addition to adopting a new FMVSS, the NPRM also proposes to amend Federal Motor Carrier Safety Regulations (“FMCSRs”) to require the AEB and ESC systems to be maintained and used during CMV operation.    

The proposal further requires heavy vehicles to be equipped with forward collision warning (“FCW”) systems as an element of the AEB system. FCW systems provide an alert to a driver of an impending rear-end collision so the driver will take action to prevent the collision. AEB systems build on the FCW by using multiple sensor technologies to sense when the vehicle is in a crash imminent situation and automatically apply the vehicle’s brakes or apply more braking force to supplement the driver’s braking.

Specifically, the proposal outlines the following requirements:

• FCW Requirement: Vehicles must provide the driver with an FCW at any forward speed greater than 6.2 mph.  The FCW must be auditory and visual.

• ESC Requirement: In an amendment to FMVSS 136, nearly all heavy vehicles must have an ESC system that meets the equipment requirements, general system operational capability requirements, and malfunction detection requirements of FMVSS 136, but not its performance test requirements. This includes previously ESC-exempt vehicles such as Class 3-6 heavy vehicles, school and transit buses, and multipurpose passenger vehicles.

• AEB Requirement: Vehicles must have an AEB system that applies the service brakes automatically at any forward speed greater than 6.2 mph when a collision with a lead vehicle is imminent.

• AEB Testing Requirement: The proposal’s test procedures include three distinct testing scenarios for the AEB system.  The tests cover scenarios in which the AEB vehicle is approaching (1) a stopped lead vehicle; (2) a slower moving lead vehicle; and (3) a decelerating lead vehicle. 

• AEB False Activation Testing Requirements: Two test scenarios must be completed to ensure the AEB system does not inappropriately activate when no collision is actually imminent.  These two scenarios are driving over a steel trench plate and driving between two parked vehicles.

• AEB System Malfunction Detection: AEB systems must be capable of detecting a system malfunction and notifying the driver of any malfunction.  However, NHTSA is not proposing a specific AEB malfunction telltale.

• FMCSR Proposal: CMVs subject to FMVSS 136 must operate and maintain AEB and ESC systems in accordance with FMCSA inspection and maintenance requirements. 

As proposed, there are no retrofitting requirements for existing heavy vehicles to install AEB or ESC for vehicles not currently subject to FMVSS 136.  Additionally, there are exemptions for certain heavy vehicles from the AEB and ESC requirements, including for vehicles with an axle that has a gross axle weight rating of over 29,000 pounds that are equipped with an air brake system, and vehicles involved in driveaway-towing operations.

The NPRM proposes a tiered phase-in schedule for the new AEB standards:

• For vehicles currently subject to FMVSS 136 (ESC systems for heavy vehicles), any vehicles manufactured on or after the first September 1 that is three years after the date of publication of the final rule would be required to meet the proposed heavy vehicle AEB standard. 

• For heavy vehicles not currently subject to FMVSS 136, any vehicle manufactured on or after the first September 1 that is four years after the date of publication of the final rule would be required to meet the proposed AEB requirements, including the requirement to have ESC systems. 

• Small volume manufacturers, final-stage manufacturers, and alterers would be provided an additional year to comply with the proposal beyond the dates identified above. Accordingly, these entities would have to meet the new requirements by September 1 four years after the date of publication of the final rule (for vehicles currently subject to FMVSS 136), or five years after the date of publication of the final rule (for vehicles not currently subject to FMVSS 136).

• For the FMCSA ESC system requirement, vehicles currently subject to FMVSS 136 would be required to comply with FMCSA’s proposed ESC regulation on the final rule’s effective date. Heavy vehicles not currently subject to FMVSS 136 would be required to meet the proposed FMCSA ESC regulation on or after the first September 1 that is five years after the date of publication of the final rule.

• For the FMCSA AEB requirement, vehicles currently subject to FMVSS 136 would be required to comply with FMCSA’s proposed AEB regulation on or after the first September 1 that is three years after the date of publication of the final rule.  Heavy vehicles not currently subject to FMVSS 136, and vehicles supplied by small-volume manufacturers, final stage manufacturers and alterers, would be required to meet the proposed FMCSA ESC regulation on or after the first September 1 that is five years after the date of publication of the final rule.

The NPRM requests comment on the following topics:

• The proposed lead time for meeting the proposed requirements

• How the lead time can be structured to maximize the benefits realized quickly while ensuring the standard is practical

• How this proposal may disproportionately impact small businesses

• Types of operations of heavy vehicles for which an exemption from the proposal may be appropriate

• What rules should apply to certain multi-stage or altered vehicles

• Whether ESC is necessary to ensure safe AEB operation, or any other reason an ESC system is a necessary prerequisite for an AEB system

• Whether ESC systems should be required to meet test track performance requirements

NHTSA may issue a final rule adopting AEB requirements for light and heavy vehicles in a single FMVSS for all vehicle classes.

Comments on the NPRM are due September 5, 2023.

Authored by Allisa Newman, Susan McAuliffe, and Valerie Marshall.