, March 15 -- Commuters in central Barcelona have had the opportunity to ride a bus free of charge this week-but with one notable difference: there's no driver behind the wheel.

The autonomous mini-bus starts and stops on its own, braking when changing lanes and smoothly cruising down one of the city's most popular boulevards.

Renault is conducting tests of its new driverless mini-bus in Barcelona, operating it on a 2.2-km (1.3-mile) circular route with four stops in the city center. Adventurous passengers can ride the bus for free during the trial.

The French automaker has partnered with WeRide, an autonomous vehicle company, to develop the prototype. After unveiling it at the French Open last year, Renault is now testing the vehicle ...