Let the automobile and fossil fuel industries pay for the roads. It was their profit whose preference built that system over more sustainable scalable options that we already had. These industries collaborated in disassembling what was, in retrospect, a wisely-conceived urban public transit infrastructure.
I suppose that everyone's hoping driverless will cars help, but I think there's a long-term stability in a larger public system than can be achieved with privately-owned vehicles for a city. Surely, no matter what, there will be a diversity of transit options as time goes on, but we're anemic on some right now. Getting these massive fleets of internal combustion engines out of the civic atmosphere will probably be of great benefit to public health along major roads.