It was at Heathrow.
As a taster, Heathrow already has a driverless vehicle system which has been operating for some time. Here is where it runs ...
All we have to do is to transfer Heathrow's "Pods" onto a real road with all the obstructions and dangers that such an environment might offer and, bingo, we have driverless buses; but small and "perfectly formed".
Tomorrow we take a short nip around the perimeter road from Terminal 5 to the Compass Centre.