FMCSA Denies Waymo and Aurora Bid to Replace Warning Triangles With Cab-Mounted Beacons

The Federal Motor Carrier Safety Administration denied a request from Waymo and Aurora Operations to let driverless trucks use cab-mounted warning beacons instead of the reflective triangles or flares required when a truck stops on a highway or shoulder. The decision was published in the Federal Register on December 27, 2024.

The request

Federal rules require the driver of a stopped truck to turn on the hazard flashers and, within 10 minutes, place warning devices at set distances behind and in front of the vehicle. The approved devices are three reflective triangles, six fusees or three liquid-burning flares. The rules also require exterior lamps to be steady burning.

In their 2023 application, Waymo and Aurora said placing triangles is "not feasible for autonomous CMVs without a human on board." They asked that they and "other similarly situated companies" be allowed to use forward- and rearward-facing amber flashing beacons mounted high on the cab when a truck is run by a Level 4 automated driving system. They also asked that the exemption "permit any configuration of similar effectiveness."

FMCSA published the application for comment in March 2023 and received 51 comments.

Why FMCSA said no

The agency said the application did not show that the beacons would provide a level of safety equivalent to or greater than the existing rules. "The application does not provide sufficient details about proposed alternative devices, and the limited data presented does not support a likely equivalent level of safety for a national, industry-wide exemption for all companies operating autonomous CMVs," FMCSA said. It added that the broad exemption "lacks necessary monitoring controls to ensure highway safety."

FMCSA found flaws in both supporting studies. The Waymo-sponsored study used 48 participants on a test track, and among respondents who chose which device was better for signaling a stopped truck, 8 out of 10 picked triangles. Aurora's on-road study involved only about 64 minutes of testing time with the beacons across eight scenarios, and beacons drew a lower response rate than triangles in five of the eight.

The agency also raised a basic placement issue. Triangles sit behind the truck, while the beacons sit on the cab, "raising the possibility that drivers see the rear of a stopped CMV before they see the beacons."

FreightWaves reported that Waymo had announced in July 2023 that it was stepping back from trucking to focus on ride-hailing.

Supporters and opponents

The American Trucking Associations, the Autonomous Vehicle Industry Association, Kodiak and other companies supported the request. Opponents included the Owner-Operator Independent Drivers Association, the Truck Safety Coalition and labor groups.

"Reflective triangles and flares are not reliant on technology systems that are so vulnerable to disruptions," OOIDA President Todd Spencer said, according to FreightWaves.

FMCSA said its decision does not stop the applicants or others from seeking an exemption to use "better defined warning beacons for specified companies in particular locations," and that it may accept a resubmitted application if the applicants address the reasons for the denial.

What it means for drivers and fleets

For drivers, the December 2024 denial meant every truck stopped on a highway, with or without a human driver, still had to be protected by triangles or flares placed behind it. For autonomous truck developers, it left an operational gap: a driverless truck that breaks down has no one on board to set out warning devices. FMCSA's reasoning pointed to what a future request would need: a precisely defined device, specific companies and locations, broader test data and reporting that lets the agency monitor results.