Some vehicles are fitted with anti-lock braking systems (ABS). Wheel-speed sensors in these systems detect the moment during braking when a wheel is about to lock. Just before this happens the system reduces the braking effort and then rapidly re-applies it.
This action may happen many times a second to maintain brake performance.
Preventing the wheels from locking means that the vehicle’s steering and stability is also maintained, leading to safer stopping. But remember, ABS is only a driver aid. It doesn’t remove the need for good driving practices, such as anticipating events and assessing road and weather conditions.
Anti-lock braking systems are commonly used on large vehicles and are required by law on some. It’s important to ensure that an ABS is functioning before setting off on a journey. Driving with a defective ABS may constitute an offence.
The satisfactory operation of the ABS can be checked from a warning signal on the dashboard. The way the warning light operates varies the light comes on with the ignition. It should go out no later than when the vehicle has reached a road speed, set to the requirements of the vehicle speed limiter.