Why does an automatic car still roll after shifting to P gear?

[DeHarley]

An automatic car may still roll after shifting to P gear because the handbrake is not engaged. The P gear position has a locking device that secures the gear, providing some anti-slip effect on the vehicle, but it cannot match the locking force of the handbrake. Moreover, if parked on a slope, shifting to P gear without engaging the handbrake can create pressure on the internal components of the transmission, potentially leading to structural damage. The P gear is the most common gear position in automatic transmission models, usually located at the front of the gearshift console, ahead of the R gear. Its purpose is to lock the axle when the car is stationary on a slope. Typically, automatic cars have six gear positions, arranged from top to bottom as P, R, N, D, S, and L. For general driving needs, only the parking gear P, reverse gear R, neutral gear N, and drive gear D are used. However, in certain special driving conditions, other functional gears may be required.