First of all, let us understand what happens when you try to brake hard in a vehicle with no ABS in low grip conditions like on snowy or wet roads. Your input on the brake pedal will apply braking action on the wheels but since there is no traction/grip of tyres in contact with the road surface, the wheels will stop rotating altogether even when the car is in motion. This is called locking up of wheels. And when the wheels lock up, it is impossible to steer away in case there is an obstacle ahead of the vehicle.
ABS works on the principle of ‘threshold braking’. The threshold braking is a driving technique most commonly used in motor racing. This technique involves the driver modulating the brake pedal pressure to maximise the braking force. The optimal amount of braking force is developed at the point when the wheel just begins to slip. The brake pedal is released when the tyres reach their slip point as braking beyond this point causes the tyre to slide. With modern electronic ABS, this is done automatically with the use of sensors and hydraulic actuators.
What ABS does is, even if you apply brakes with your right foot pinned to the floor, it senses the abrupt slowing down of wheels. And instead of braking the wheels in a single go (which we know will lock up the wheels), it brakes it intermittently. In simple terms, even if the brake pedal is fully pressed because of panic braking, the brakes go – on-off-on-off-on-off and so forth.
This can happen around hundreds of times in a single second and therefore when ABS is in action, you get a ‘pulsating’ feeling on the brake pedal. So by doing this intermittent braking, the ABS directly prevents the wheels from locking up. Also, you can steer the vehicle away from any obstacle while braking, thanks to the prevention of lock-up by ABS.