PARIS (Reuters) - Cars that drive themselves could be on the roads four years from now, provided red tape does not get in the way, Mr Carlos Ghosn, head of the Renault-Nissan alliance, said on Tuesday.

Silicon valley companies have long pioneered "autonomous vehicles", and Google tested one in Nevada in 2012. German luxury carmaker Mercedes-Benz developed an S-class limousine that drove in August without any driver input.

Renault has created the Next 2 prototype version of its Zoe model which enables drivers to let go of the controls at speeds below 30 kmh thanks to GPS positioning, cameras and sensors, though a human must stay behind the wheel. "The problem isn't technology, it's legislation, and the whole question of responsibility that goes with these cars moving around... and especially who is responsible once there is no longer anyone inside," Mr Ghosn said at a French Automobile Club event.

The first cars could hit the roads in 2018 in the "pioneer countries" of France, Japan and the United States, with commercialisation starting across Europe in 2020, the chief executive said.

An amendment to United Nations rules agreed earlier this year would let drivers take their hands off the wheel of self-driving cars. The change was pushed by Germany, Italy and France, whose high-end carmakers believe they are ready to zoom past United States tech pioneers to bring the first vehicles to market.

Provided the amendment clears all bureaucratic hurdles, it would allow a car to drive itself, as long as the system "can be overridden or switched off by the driver".

A driver must be present and able to take the wheel at any time.