A lot of work to do exactly as you'd need to break down by type of vehicle.
But we used 560 million tonnes of Carbon which I make approximately 90 billion litres of petrol/diesel let's be daft and assume everybody gets 10Km per litre that's 9 billion Km.
the Tesla motors sports car is probably the most advanced car today and it does 220 miles (350Km) between charges. and takes 56KWhr to charge.
So we have an estimate of about 1.5 billion KWhrs extra. So say 200 million KW extra
Which is about 200 extra Sizewells
Now there's a lot of silly assumptions there
We've assumed all little sports cars and no lorries and ignored transmission losses. But we've also neglected the fact that most charging is overnight when generation capacity is underused.
Remember too that making such calculations at this point is like Edwardians calculating petrol requirements and saying the internal combustion engine will never catch on.
One final point about Fusion - It may be 40 years away but it is the only scalable long term energy proposal and it is now progressing.
Jet achieved ignition and ITER in France will achieve Breakeven. Finally DEMO - Probably in Japan will be the first power station in about 40 years for more see
http://www.iter.org