Emergency braking of the heavy duty vehicles, especially the combinations, can be dangerou$, particularly on wet or icy roads having a low coefficient of adhesion. Locking of the wheels having important consequences, loss of the trajectorye ontrol, jackknifing, slipping of the trailer, the equipment and car manufacturers have devcloped the antilock devices.

Some requirements exist since 1972 into the regulation 13 (ONU). The series fitting of the vehicles effectively started in 1980 and the experience permitted to complete these requirements in 1983 (EEC Directive 85/647).

The requirements ask to keep a good braking efficiency, a good stability, a low compressed air consumption and no wheel locking.