Why does an automatic car still roll backward when in D gear?

[SanLawson]

Rolling backward during hill starts is unavoidable and a normal phenomenon. Here are the relevant explanations: 1. Automatic transmission: As the name suggests, automatic transmission doesn't require the driver to shift gears manually. The vehicle automatically selects the appropriate gear based on driving speed and traffic conditions. A typical automatic transmission car has six gear positions, from top to bottom: P, R, N, D, S, L. 2. Hill start assist: Also known as Hill-start Assist Control. To prevent difficulty when starting on an incline, the hill start assist control temporarily applies brakes to all four wheels (for a maximum of about 3 seconds) to prevent the vehicle from rolling backward.