EV's are better than fossil cars, but they too have most of their emissions in operation rather than manufacturing.

So the significant question isn't "will driverless lead to fewer emissions because of fewer cars", the significant question is "will (electric) driverless lead to fewer emissions because of fewer miles driven?"

It's no question that electric is more efficient on emissions per mile, but if the number of trip-miles increases because driverless cars eg are constantly circling the downtown waiting for passengers, or they make more low-occupancy trips possible so they induce demand of low-occupancy miles, well it could be worse emissions wise!