Which commercial vehicles were first required by the Department of Transportation to be equipped with antilock braking systems (ABS), effective for vehicles built on or after March 1, 1997?

49 CFR 393.55 (ABS equipment requirement); FMVSS No. 121, 49 CFR 571.121 (air brake ABS performance standard); AAMVA CDL Manual Sec. 2.18.2, p.2-35

The staggered implementation dates mean many older vehicles still legally on the road lack ABS entirely. Knowing which vehicle types and ages the requirement covers helps a driver understand why checking for a malfunction lamp matters differently depending on the vehicle.