Will robot drivers rule the road?

It was on the motorway near Phoenix, Arizona, that I realised fully driverless cars might be quite a distant dream. And that was because our Google Waymo robo-taxi seemed incapable of leaving that motorway. We were in Arizona to record a radio documentary for the BBC World Service about the progress towards creating autonomous vehicles that would make our roads safer and replace human drivers with robots. Google leads this race at the moment and for the past six months has been offering a robo-taxi service, Waymo One, to a select few early adopters in and around the Phoenix suburb of Chandler. Our first ride with Waymo took us through the quiet suburban streets, where traffic is sparse and drivers well mannered.