[johnm1019]

Consider that taxpayers fund and build airports. Available seats on an airplane are priced using demand based pricing.

Taxpayers provide land and (sometimes) fund rail infranstructure. Most long distance rail uses demand based pricing (the last seat costs more than the first).

Taxpayers also (sometimes) provide/pay for land and the costs to build roads. Until now, we haven't seen demand based pricing (the last slot costs more than the first), but it actually fits well with other modes of taxpayer funded transportation.

This approach also considers the cost and value of a road network in a congested area. This could possibly fund other new transport in the area if it really is such a valuable commodity.