Shiftlock-interlock.: Shiftlock is a safety feature in automatic transmission systems. It makes sure that the gearshift lever can be moved from neutral (N) or park (P) into a drive gear (D or R) only if you hold down the brake pedal. Interlock is an additional safety function that prevents loss or unintentional removal of the ignition key while driving: the ignition key cannot be withdrawn without having the gearshift being in park (P).