There is a good case for free urban mass transit, but the effect it would have on highway congestion is problematic. There is the well-known Anthony Downs theorem that cars will always fill up the highways to take up any slack created by policy measures.
The late and lamented Nobelist Bill Vickrey foresaw a scheme to charge drivers with automatic scanning devices, depending on where they drove (and when, and how often) and send them a bill each month. This was thirty years ago. We're at the point where they are used for toll-taking.
The regressivity of the gas tax is true but irrelevant; any such tax could be compensated for in the income tax. How effective it would be is another matter.
mbs
Car drivers pay road tax, petrol tax and now mooted congestion charges. They are subsidising the middle class professionals who commute by rail from the South East to London's financial district. As has already been pointed out, the petrol - sorry gasoline - tax is a regressive tax on working families. -- James Heartfield Sustaining Architecture in the Anti-Machine Age is available at GBP19.99, plus GBP5.01 p&p from Publications, audacity.org, 8 College Close, Hackney, London, E9 6ER. Make cheques payable to 'Audacity Ltd'. www.audacity.org