What is the primary function of the Anti-lock Braking System (ABS) in a vehicle?

1. To decrease the braking distance on all road surfaces.
2. To prevent the wheels from locking up during emergency braking, allowing the driver to maintain steering control.
3. To automatically apply the brakes on the driver's behalf whenever the on-board sensors detect that a crash is imminent.
4. To lock the wheels to stop the vehicle faster.