The AAA, a US consumer and travel services organisation, said current assisted driving and automated braking systems fall short of true autonomous driving, and require drivers to stay in control of vehicles.

The organisation has backed these claims by the performance of assisted driving systems installed in Tesla, Hyundai Motor and Subaru cars in recent tests, in which all vehicles failed to avoid head-on collisions. Tesla's Autopilot system, however,  did slow the vehicle to a walking speed before striking an oncoming foam car model.

A fast-growing number of new vehicles are equipped with Automated Driver Assistance Systems (ADAS), which serves to partially automate functions such as steering, staying in a lane and braking. Tesla's Autopilot is one of the best-known such systems, but most major automakers offer similar technology.

Regulators, automotive insurers and carmakers have long warned that ADAS systems cannot safely substitute for a...