From Fed govt data,For what its worth here is an article for PTUA on the cost of road transport. THe article goes in considerable detail of the problems of finding road transports true cost.The reality is that roads are paid for by users, as reflected in BITRE statistics.
One of the main problems in this argument is that in our society road transport is so widely used most people will go to significant lengths to minimise its cost.
Its widely believed though that road transport costs are considerably than the funds raised from fuel taxes.
Additionally, one needs to considers that local roads (eg. council funded) exist for purposes beyond transport (eg. access) and are required regardless of road use, and those statistics do not include any revenue from municipal sources.
By comparison, rail does not pay it's way - revenue need not meet expenditure (since the benefit of public transport use is reduced road expenditure), but even considering that, passenger contributions fall far short of necessary. Rail cost recovery in Melbourne is only about 20%, in London it is closer to 90%.
What needs to change is the manner in which that revenue is collected, since at the moment expenses like registration unfairly favour those that use their cars more often, whilst fuel taxes advantage the wealthier who can afford more fuel efficient vehicles, whilst particularly disadvantaging those who may need to travel longer distances, but contribute in a limited manner to congestion (eg. regional and outer suburban users).
Fuel excise has dropped from 1.6% of GDP in 2001 to ~1.0% last year.
Fuel economy improving by ~10% per decade for last 20 years, however expected to increase rapidly with Hybrid and EV technology roll out. Australia expected to have 20% EV by mid 2030's.