States are generally prohibited from tolling previously free portions of the Interstate Highway System, under the view that the road has already been paid for. There is currently one exception to the rule and more states are expressing interest in using that exception. In 1998 Congress created a pilot program to allow up to three states to begin collecting tolls on existing interstates to fund improvements on those highways. Although both Virginia and Missouri have received federal permission to proceed with an interstate tolling plan, neither state has yet implemented tolls on its interstates.
However, the current economic downturn has spurred interest in tolling interstates in a number of states, and Rhode Island is currently developing a tolling plan for Interstate 95 under which toll revenues would go towards improvements on the highway. Giving states the ability to toll interstates is one way that the federal government could create a new funding source for states, allowing states to develop funding measures that work for a particular locale.
For more information see Daniel Vock’s recent article, “States push to convert interstate highways into toll roads”, at Stateline.org.