Yesterday, Mercedes-Benz demonstrated such a car - an S-class fitted with a radar-based system known as Distronic Plus.

It can follow a car ahead of it without the driver touching either the brake or accelerator.

It speeds up, slows down and even stops in tandem, even at speeds of up to 200kmh. And if another vehicle cuts into its lane, the S-class will automatically apply the brakes to keep its pre-set distance.

Besides making stop-start commutes more bearable, the system has safety applications too. The demo S-class was made to head straight for a soft obstacle.

When the car senses a collision is imminent, it beeps loudly before applying 40 per cent of the brake power to mitigate the impact. In the same split second, it tightens all the seatbelts onboard to brace the occupants for the 'crash'.

Why does the car not stop by itself?

'We want to give the driver full control,' said Mr Stefan Hahn, senior manager of group research and advanced engineering, DaimlerChrysler. 'A car that stops in such a situation would be impossible to drive,' he explained because the system cannot tell the difference between a tree branch, a kerb or a pedestrian.

Mercedes expects to introduce cars with Distronic Plus here as early as year-end. The feature is estimated to cost $11,000 to $12,000.

CHRISTOPHER TAN