It works like this. A radar in the car's grille detects the position of anything in a wide-angled sweep ahead; a camera decides what that object is; and if there's a danger of a collision, the driver is warned to take action.
If there's no response, the car brakes itself to a standstill when the speed is below 22mph, or by enough to minimise the impact severity if it is travelling faster.
Volvo warns that the system has 'the same limitations as the human eye' in darkness or bad weather, and it can't reduce stopping distances. What it can do, though, is to significantly reduce reaction time.
Left: The system uses a camera in the interior mirror