With increasingly fuel-efficient cars, gas taxes are an ineffective way to pay for roads. Gas taxes are also collected mainly by federal and state governments, requiring local governments to find nearly $30 billion per year in general funds to subsidize roads. Mileage-based fees would eliminate congestion and solve these problems, as well as allow private parties to build or take over some roads. In any case, the growing use of tolls means the federal government has a declining role in highway funding.