New Delhi, Sept. 4 -- The US National Highway Traffic Safety Administration has opened an investigation into the certification of nearly 1,000 Tesla Cybercabs, putting the electric vehicle maker's newly launched driverless taxi programme under immediate regulatory scrutiny.

The investigation began as Tesla started commercial deployment of a small number of the two-seat Cybercabs in Austin, Texas, on Thursday. The company has said it intends to expand the service gradually, adding more vehicles and eventually taking the robotaxis to other locations.

At the centre of the NHTSA inquiry is a basic question: how did Tesla certify a vehicle designed to operate without a human driver when it does not have the conventional controls normally ass...