Mercedes believes such a car would help take the stress out of urban travelling - it would become a cruise control for the city.

Two cameras provide a stereoscopic view

The system uses a pair of cameras mounted just behind the windscreen to lock onto any moving object in front - it could be another car or even a pedestrian.

The stereoscopic view is sent to a computer which calculates how fast the car should travel and in which direction. The electronic brain also determines a safe distance from which to follow the leading object.

It has a number on in-built safety measures. A colour camera can recognise traffic lights and warn the driver that the vehicle must stop. The computer even carries a database on human legs movements so that it can bring the car to a halt if a pedestrian steps out into the road.

Research work

The prototype still needs more development work. When the BBC tested the car for its science series Tomorrow's World, the car sometimes had difficulty following other vehicles that made sharp turns.

Dr Franke: Confident problems can be sorted out

The system can also be upset when a third vehicle goes into the gap between the prototype and the lead car.

The tracking system has even been known to turn its attention to fences and tress. But Mercedes believes these problems can be overcome.

"What we want to do is to assist the driver," said Dr Franke, the man leading the research, "help him manage difficult situations. In the far end 20 to 30 years, it might be possible for all cars to go autonomously.

Dr Franke is so confident in his research that he regularly takes the prototype on the open roads of Germany.

"I drive autonomous cars with my family. Maybe this will convince you."