FMCSA advances study on whether warning triangles behind stopped semi trucks ‘meaningfully’ improve safety
The Federal Motor Carrier Safety Administration (FMCSA) announced that it is moving ahead with a study examining the effectiveness of commercial vehicle drivers deploying warning devices like triangles on overall roadway safety.
The FMCSA provided new details on the “Study of Warning Devices for Stopped Commercial Motor Vehicles” in a Federal Register Notice published on December 23, 2025.
The “experimental” study will evaluate “whether warning devices meaningfully influence crash-relevant aspects of human performance in the presence of a parked or disabled commercial motor vehicle (PDCMV), and if so, how and to what extent.”
The agency plans to conduct a study using 256 drivers at a “closed-course, state-of-the-art driving research facility that will allow the most comprehensive examination of the effects of warning devices to date.”
“Public interest in warning device requirements for PDCMVs has increased in recent years for several reasons. For example, advances in automated driving system (ADS) technology have raised critical questions regarding potential barriers to regulatory compliance with warning device safety standards and regulations which reference or require a “driver.” In addition, alternative types of warning devices developed by industry, including those intended to increase driver safety during device deployment, have resulted in multiple applications for exemption from the corresponding safety regulations. These recent issues related to warning device requirements also call attention to the historically unresolved questions of whether the use of such devices improves traffic safety and, if so, how and to what extent,” FMCSA said.
“Given the increasing focus on ADS, questions surrounding the safety of CMV drivers when deploying warning devices, and the availability of new technology and alternative devices since these questions were last explored in the 1980s, there is a need to thoroughly evaluate the effectiveness of warning devices under current regulations,” the agency noted.
Results of the study will inform future rulemaking related to warning devices and “provide baseline data necessary to inform Agency decisions on exemption applications for alternative warning device products.”
In October 2025, autonomous driving technology company Aurora announced that it had been granted an FMCSA exemption allowing the company to use cab-mounted warning beacons as an alternative to reflective warning triangles. The exemption was granted after Aurora filed a lawsuit against FMCSA.
The FMCSA first announced the study more than a year ago in a Federal Register Notice published on January 8, 2025.
FMCSA will accept public comment on the study through January 22, 2026. You can click here to leave a public comment.