Anti lock brakes are vehicle brakes used as part of a comprehensive braking system that is meant to aid in stopping cars, trucks and other types of automobiles in emergency situations. The brakes function by preventing the braking system, in most cases, from completely locking up the tires. They are meant to prevent a car from skidding, which not only negatively affects directional control but also stopping control.
The vast majority of new cars now have anti lock brakes installed as a standard vehicle safety feature. The fact that they are considered far safer than traditional brakes also means that cars that feature them are usually given a discount on auto insurance rates. However, the more important reason to have these brakes is because of the control they provide in emergency situations.
When an unexpected situation comes up, drivers often go into panic mode. In this situation, the first instinct is to stop the vehicle as quickly as possible, in most cases. To do that, they often press has hard as possible on the brakes in an instinctual reaction. In the the past, with traditional braking systems, this would cause the brakes to lock up. Anti lock brakes ensure that does not happen, or at least does not happen as often.
This type of brake operates under a very complex system, and some would say that once the system is actively controlling the situation, it is out of the driver's hands. The electronic control unit monitors the rotation of the wheels and when a difference in the rotational speeds of the wheels is detected through the use of sensors, it will act to decrease the braking pressure on those wheels rotating slower, thus naturally speeding up their rotation.
The idea behind anti lock brakes is similar to the idea of "pumping" the brakes in traditional braking systems. Pumping the brakes helps keep the rotational speed of each wheel in sync. However, with this type of brake system, pumping should not be done, simply because you are working against what the brakes are already trying to do.
Despite the fact that anti lock brakes are widely used and considered an indispensable safety feature in many vehicles, there are conflicting studies about their actual effectiveness. An Australian study suggests they do help reduce multiple-vehicle crashes significantly. However, a study by the Insurance Institute for Highway Safety suggests that they do not reduce the risk for a fatal accident.