National Journal: Should Existing Interstate Highways Be Tolled?

From National Journal: 

...Yet the cost of bringing the nation's roads and bridges into a state of good repair far exceeds the revenue raised by the Highway Trust Fund -- a gap of up to $240 billion annually through 2020, according to the National Surface Transportation Policy and Revenue Study Commission. Especially in this era of tight federal and state budgets, should states be given greater leeway to toll existing federal-aid interstate highways? What about just tolling new capacity? Or should tolling federal roads continue to be restricted since the public already pays for them with their fuel taxes?