A little-noticed amendment to the United Nations Convention on Road Traffic agreed last month would let drivers take their hands off the wheel of self-driving cars. It was pushed by Germany, Italy and France, whose high-end carmakers believe they are ready to zoom past American tech pioneers and bring the first "autonomous vehicles" to market.

"Today I am only allowed to take my hands off the wheel to a limited extent. Thankfully the Vienna Convention on Road Traffic has been changed," said Thomas Weber, head of Group research at Daimler and head of development at Mercedes-Benz.