If you were to pull the handbrake on an automatic transmission car while driving at a speed of 60 km/h (or any significant speed), it would have several immediate effects:
Sudden deceleration: The handbrake is designed to apply a strong braking force to the rear wheels. When pulled while driving, it would result in a sudden and forceful deceleration of the vehicle. This abrupt change in speed can cause a loss of control over the car, potentially leading to skidding or spinning.
Rear-wheel lock-up: The handbrake primarily affects the rear wheels. Applying the handbrake while driving could lead to the rear wheels locking up, which can result in a loss of traction and stability. The car may fishtail or rotate uncontrollably.
Damage to the braking system: The handbrake is not designed for use while the car is in motion. Applying the handbrake while driving at a significant speed can put excessive strain on the braking system, potentially leading to damage or failure of the brake components.
Increased risk of accidents: Pulling the handbrake while driving can significantly increase the risk of accidents. It can destabilize the vehicle, cause loss of control, and make it difficult to steer or maneuver safely. Other drivers on the road may not anticipate such sudden and unexpected actions, leading to collisions or other dangerous situations.
In summary, it is highly dangerous and not recommended to pull the handbrake while driving, especially at higher speeds. The handbrake should only be used when the vehicle is stationary or during parking. In emergency situations where you need to slow down or stop the car quickly, it is safer to use the foot brake and gradually reduce the speed while maintaining control of the vehicle.