On the road in San Francisco, riding in a driverless taxi

Perched on the edge of a curb, squinting down the length of Market Street in the US city of San Francisco, I find myself twitchily tapping my phone, only to wince as the time ticks away. And up the Market Street rail line rumbles my deliverance: a 1928 wood-panelled tram in green-and-white trim. Oh, the irony: I'm headed to test out one of the city's newest transportation options while creaking down the road on one of its oldest. San Francisco has long been a hub for transportation innovation. It was here that the first cable car system was put into use.