This is an unmitigated good. Limited-access roads are luxuries of transportation, much as high-speed rail is a luxury on top of highly-interconnected intercity rail. There is no reason Interstates should be free: they should have user fees levied on them. The U.S. Road network predates and shadows the Interstates and is not exclusively limited-access--they can be used to get around the country if one is unwilling to pay tolls. There is no reason a gas tax, a tax levied on all drivers, should be used to fund the Interstates, a luxury for a select few drivers, either. Interstates should do what they have never done--pay for themselves, by costing those who take advantage of the system. Europeans understand this: ever wonder why European motorways are nearly always tolled? Our Interstates are, ironically, a socialist system, a conversion of a luxury into a commons.
Better still than leasing the Interstates: why not sell them wholesale? Roads like the Schuylkill and the Blue Route must be worth a mint: we can sell this mature system and use the money to get to work building its competition. Rail and bikes are in; roads are out.