What system temporarily holds brake pressure when starting on a hill to prevent rollback?

The system that temporarily holds brake pressure when starting on a hill to prevent rollback is hill start assist.

Hill start assist detects that a vehicle is stopped on an incline and keeps the brakes applied briefly after the driver releases the brake pedal. That pause gives the driver time to move to the accelerator—or, in a manual car, coordinate the clutch—without the vehicle rolling backward. The exact activation threshold and hold time vary by manufacturer.

The idea has a long history. An earlier mechanical version, commonly called a hill-holder, was introduced as an option on the 1936 Studebaker President. Bendix later marketed a related system under the name NoRoL, and similar devices spread to other makes. Modern systems usually use electronic brake control and sensors that monitor incline, wheel speed and pedal input.

Hill start assist is not the same as downhill assist, which controls speed while descending. Brake assist is designed to increase braking force during emergency stops, while traction control limits wheelspin. Hill-start systems may be known by names such as hill-hold control, hill-start assist control or HAC.