The brake system transmission interlock prevents inadvertently shifting the automatic transmission of a vehicle out of park. This system requires the driver to press the brake pedal in order to move the gear selector out of the park position.
The National Highway Safety Commission reached formal agreement with domestic and international automakers in 2009 that all vehicles sold in the United States were to include this safety interlock. When the driver shifts a car into park, a rod presses a mechanism into place to prevent it from moving. The design of the interlock is to prevent individuals from moving the gear selector out of park, which causes the car to roll.