When an ABS (or antilock brake system) is in operation, the driver will feel _________.

An antilock brake system is a safety system that prevents car wheels from locking up. This helps a driver avoid uncontrolled skidding and maintain control of the vehicle. The system works in the following manner: sensors notice when one wheel is about to lock up (usually when it is deaccelerating rapidly). Then, pressure is reduced to that brake, then increased, then decreased, etc. This causes the pulsing feeling in the brake pedal. This ensures that the tire slows down at the same time as the car and does not lock up.