Which is always easier said than done and a bit simplistic. The primary factor derived to date has been to tie the wear factor to axle weight. Meaning an empty vehicle made for transporting goods would be in the range of passenger vehicles. In addition to simple overloading, improperly balanced loading represents more damage for the same total vehicle weight. So each axle must be weighed in a loaded state on each individual trip to determine the presumptive proportional tax burden.

All of which creates overhead in the form of people to be paid, equipment to build/own/maintain, time lost at all stages, the usual political influence problems, jusrisdiction of different areas of road, implementing policy, and corruption. Most of it will end end up as pass through cost to individuals either way as both consumer goods and roadways are deemed essential. It's ultimately a fairness exercise of tax distribution so like most things in the public interest the arena any idea must be fought in is politics.