An anti-lock braking system (ABS) is a system that prevents the wheels from locking while you are braking. It is a very safe and effective system and the purpose of this is twofold: it allows the driver to maintain steering control under heavy braking and, in most situations, it shortens the braking distance (by allowing the driver to hit the brakes really hard without losing control of the vehicle).
If you have a vehicle that does not have an anti-lock braking system, you can manually pump the brakes to prevent the wheels from locking up. Whereas, in vehicles that are equipped with an anti-locking brake system, the drivers foot needs to remain firmly on the brake pedal, and this will allow the system to automatically pump the brakes.
A typical anti-locking braking system (ABS) has a central electronic unit. The electronic unit has four speed sensors for each wheel as well as hydraulic valves on the brake circuit. The electronic unit will constantly monitor the rotation speed of each of the wheels. When it senses that a wheel might be rotating slower than the others, it will decrease pressure on the brakes. This will reduce the braking force on that wheel and it will cause a pulsing feeling through the brake pedal.
If the sensors become contaminated with metallic dust, it will fail to detect any wheel slip.
On most surfaces, ABS equipped vehicles are able to achieve braking distance shorter than those without. In most conditions, ABS will reduce the drivers chances of crashing. A skilled driver who isn’t using ABS, can use techniques like cadence braking (technique used to stop the vehicle more quickly on a slippery surface) or threshold braking (the driver adjusts the control of the brake system in an attempt to maximize the braking force of the vehicle) to be able to match or even beat the performance of an average driver that has ABS. In emergency situations, ABS will reduce the chances of skidding and losing control.