"We’re told by the G-drive gushers from Mountain View that road trains or platoons of driverless cars will use roads more efficiently because they’ll be able to drive more closely together than human-controlled vehicles. Right. So you’re driving along at 60mph and come across a slower platoon of some twenty vehicles moving at 55mph. You overtake them, noticing there’s no gap between each car in the platoon that’s large enough to let you in, and then you come up to the exit ramp you need to take but can’t get onto it because the platoon prevents you passing though it."
Good point, but think about it - how does sat navs (even ones going back from the last decade) do when you miss your turning? They reroute. It'll clearly be the same here.
"The cars use GPS to locate themselves, with more precise location data provided by the LIDAR and other sensors. Sensor input is received and processed, we understand, by a quad-core x86 processor using a modified version of Ubuntu Linux.
What happens when the GPS data is unavailable, as with a long tunnel? Does the car get lost?"
Again, what do sat navs do in tunnels? Use "Dead Reckoning" - it already knows it's in a tunnel because the map data is already in it's system, so it simply judges where it is by the current speed via GPS just before it went into the tunnel (which will be far far easier in a car because it will be able to rely on the car's speedometer directly and not on the speed upon entering the tunnel).
So good points, but took me not even a second to work out, so Google's engineers would have clearly already thought of this.