I just looked at the Wikipedia entry on fuel taxes, and saw the following (http://en.wikipedia.org/wiki/Fuel_ta..._United_States).
US Average $0.47/gal (includes federal and state taxes) as well as this
A 2003 Federation Highway Administration study found that 94% of federal roadway funding came from fuel taxes, 86.3% of state roadway funding came from fuel taxes, and 11.1% of local roadway funding came from fuel taxes.
The study found that altogether in the U.S., 69.6% of roadway funding ($79.6 billion) came from fuel taxes and 30.1% ($33.4 billion) from other funding sources.
So, if gas taxes are raised to make them the sole source of road funding, we're looking at an additional tax of around $0.141 per gallon. Not a large number, and not a number that would change behavior to any significant extent. If we add a "fudge factor" to account for possible reduced consumption and inflation (since the study was conducted in 2003) and make the additional tax $0.20/gal, we still would not have a price that would drastically alter behavior.
So, how did/do the European countries justify their sky-high gas taxes? Political feasibility aside, surely there was/is some justification besides just making drivers pay for the road. IIRC even if we add the classic "greenhouse gas" tax (justified based on Carbon prices) on top of everything, we'd still be at around $0.30/gal or so; still no dramatic change in behavior expected.
Ultimately, my guess is that something other than the relative high cost of driving will be needed to get people to ride more.