The Audi Adaptive Cruise Control (ACC) system regulates your car's speed and distance from the vehicle ahead. For use on vehicles with an S tronic gearbox, ACC ‘stop and go’ uses radar sensors to detect objects ahead. This can be up to 250 meters (820.21 ft) away from the car. The driver can adjust this distance and the control dynamics in multiple levels.
In stop-and-go traffic, the system can bring the car to a complete stop. After a brief stop, like at a traffic light, it automatically drives off, following the vehicle ahead. After longer stops, the driver simply has to tap the accelerator pedal or briefly activate the control stalk to resume driving.
Article source: www.audi.co.uk