A new report recommends replacing the state gas tax with mileage-based user fees to fix Michigan’s roads.

In the study, “Michigan’s Road Forward: Replacing the Fuel Tax with Mileage-Based User Fees,” researchers from the Mackinac Center for Public Policy and Reason Foundation examine the state’s road funding system.

“Raising revenue for roads through fuel taxes is unsustainable,” University of Michigan-Flint economics professor and study co-author Chris Douglas said in a statement. “Mileage-based user fees create a more equalized and sustainable way to pay for public roads.”

The study says using fuel tax revenue to fund roads repair eventually fails because of climbing fuel efficiencies and more electric vehicles on the road that don’t pay gas taxes but do pay for registration and other costs.