Under federal regulations, antilock braking systems (ABS) are required on truck tractors with air brakes built on or after a specific date, and on other air-brake vehicles (trucks, buses, trailers, and converter dollies) built on or after a later date. What are these two mandatory equipment dates?

AAMVA CDL Manual, Section 5, subsection 5.1.16 (p. 5-4)

Knowing these dates helps you understand why some older trucks and trailers on the road still don't have ABS — it's not necessarily broken equipment, just a vehicle built before the requirement applied. Drivers need to check the certification label or look for ABS malfunction lamps rather than assume every vehicle has, or needs, the system.