On a PRNDL selector, Park locks the transmission output shaft with a parking pawl. The pawl engages a notched parking gear connected to the output shaft, preventing the shaft and driven wheels from rotating freely.
Park also disengages the transmission from the engine, much like Neutral, but it adds a mechanical locking function. Because the pawl is not intended to replace the vehicle’s service or parking brake, drivers are generally advised to set the parking brake as well, especially on slopes.
Most familiar automatic selectors place P at the front or top of the pattern, followed by R, N, and D. Some older automatics lacked a dedicated Park position, so they relied on Neutral and a parking brake; transmission layouts were later standardised more widely.
A common misconception is that Park directly clamps the wheels. It actually locks the transmission’s output shaft, which normally prevents the driven wheels from turning. The parking pawl can be heavily loaded if a vehicle rests against it on a steep incline, which is another reason to use the parking brake.