I imagine the ideal situation would be a hybrid. Trains for the bulk of transport and self driving cars for the large tail of odd trips. When you want to get home from your friends house at 1AM there is no traffic on the roads, and taking PT is a 1+ hour trip while uber is 10 minutes. There will never be super fast PT connecting every odd route that runs frequently all through the night.

Cars could be radically reimagined for this use case to be much smaller and more efficient to be more like an ebike with a box around it for weather proofing.

I guess we can use a bit of 44 petawatts of solar energy reaching Earth in electric cars.