For heavy on-highway vehicles, preventing the drive axles from locking is key to vehicle stability. This paper presents a simple and reliable system to assist the driver in bringing a vehicle to a controlled stop. Design priorities are based on providing vehicle stability while maximizing system and component reliability. The result is a simple system with a single sensor and digital controller, installed integral to the drive axle, that yields a cost efficient solution to the jackknifing problem. Specific improvements in reliability, RFI immunity, and self-diagnostics over earlier FMVSS 121 systems are presented. A description of the system, development test information, and preliminary field test results are also presented.