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Person transport by rail and self-driving cars are hardly substitutions but rather complements. The wave of self-driving will, I think, hearald a new wave of rail as personal ownership of motorcars goes the way of the horse drawn buggy. Cars won't take one from London to Cambridge. Trains-- or self-driving buses-- will.
Lacking the demand for parking places will mean that few if any motorcars will be private but find usage patterns like taxis. More problematic, I think, will be transport of goods as rail will find it also difficult to complete with fleets of linked road trains (mega-trucks). Railways are currently not doing well with freight and I suspect the conflicts will increase.
http://www.christianwolmar.co.uk/2016/08/rail-808-driverless-cars-going-nowhere-soon/