Eliminate the gas tax entirely and replace it with a weight and mileage based tax on commercial freight shipping.
Cars put next to no strain on the roads. Freight trucks put a disproportionate amount of strain on the roads.
https://www.gao.gov/products/109954
a five-axle, tractor-trailer loaded to the 80,000-pound Federal limit, has the same impact on an interstate highway as 9,600 automobiles
a truck axle carrying 18,000 pounds is only 9 times heavier than a 2,000-pound automobile axle, it does 5,000 times more damage
https://en.wikipedia.org/wiki/Fourth_power_law
Since the roads have to be built to tolerate trucks, the impact of the cars on the road are effectively negligible. We also already have a system for regularly weighing and monitoring the millage on freight trucks.