The National Highway Traffic Safety Administration (NHTSA) has released a significant new  rule requiring automatic emergency braking (AEB) systems on all light vehicles.  The rule is aimed at reducing the frequency and severity of rear-end and pedestrian crashes, consistent with the Department of Transportation’s zero fatalities goal under the National Roadway Safety Strategy.

The rule establishes a new Federal Motor Vehicle Safety Standard (FMVSS) 127 requiring AEB systems on light vehicles (passenger cars, trucks, buses and multipurpose passenger vehicles of 10,000 pounds or less).  FMVSS 127 also requires forward collision warning (FCW) and pedestrian AEB.  The new FMVSS implements a mandate in the 2021 Infrastructure Investment and Jobs Act (IIJA) that the Department of Transportation promulgate a requirement that all passenger cars be equipped with AEB and FCW systems.  The rule sets performance standards for these systems and – going beyond the IIJA mandate – also requires pedestrian AEB (PAEB).

The final rule follows a 2016 voluntary commitment by vehicle manufacturers to include low-speed (under 25 mph) AEB as a standard feature in new vehicles by September 2022.  NHTSA believes that the new standard is needed to ensure minimum performance standards are met, prevent or mitigate crashes at higher speeds, and address market gaps.  The agency issued a proposed AEB rule in June 2023.

Under the new FMVSS 127, AEB systems must detect and react to an imminent crash with both a lead vehicle or a pedestrian.  FMVSS 127 requirements include:

• The obligation to provide the driver with an auditory and visual FCW at any speed above 10 km/h (6.2mph) and less than 145 km/h (90.1 mph) when a collision with a lead vehicle or pedestrian is imminent.  NHTSA is requiring a standardized FCW telltale.
• The requirement that the AEB system apply the brakes automatically at these speeds when a collision with a lead vehicle is imminent, and at any forward speed greater than 10 km/h (6.2 mph) and less than 73 km/h (45.4 mph) when a collision with a pedestrian is imminent.  NHTSA added the upper speed limitations for both FCW and AEB in response to comments on the proposed rule that the requirement was otherwise open-ended, providing significant challenges for product development. 
• Test procedures that require the AEB and PAEB system to prevent the vehicle from colliding with the lead vehicle or pedestrian under certain conditions.  Lead vehicle testing is conducted under three different scenarios: lead vehicle stopped, decelerating, or slower-moving.  Pedestrian tests are done under both daylight and darkness conditions, while lead vehicle testing is only required under daylight conditions.
• False activation tests, in which the vehicle is not permitted to brake in excess of specified amounts. NHTSA rejected commenters’ suggestions for documentation or data storage requirements in lieu of tests to ensure that AEB systems will not provide unwarranted engagement.
• Malfunction detection, with a visual warning to the driver of any AEB system malfunction or failure to meet performance requirements, such as when there is a component failure, sensor obstruction, or environmental limitation. The agency is not requiring a specific malfunction telltale, in contrast to the FCW telltale requirement.
• A deactivation prohibition, which means that manufacturers cannot install a control designed for the sole purpose of deactivating the AEB system, except for certain law enforcement vehicles.  Controls that have the ancillary effect of deactivating the AEB system, such as when operating in “tow mode,” are allowed.

In response to comments that vehicles with automated driving systems should be exempt from some or all of the new FMVSS 127 requirements, NHTSA stated that it is finalizing the rule to apply to all light vehicles but will consider future modifications for ADS-equipped vehicles as needed under separate rulemaking efforts.

NHTSA added more lead time from the proposal, and eliminated the proposed phase-in approach.  Under the final rule, compliance is required by September 1, 2029.  Small volume manufacturers, final stage manufacturers and alterers will have an additional year to meet the new requirements, until September 1, 2030.

Next Steps

The rule has not yet been published in the Federal Register.  A pre-publication copy is available here.