Seems like that would only apply to highways. The average neighborhood road sees zero truck traffic, so 100% of the road wear is done by cars.
Re:Test drive of a petrol car
by toomuchtodo on Monday May 04, 2015 @12:41PM
(#9487257)
Which is why the average neighborhood road is overhauled far less frequently than highways.
"Heavy trucks obviously cause more road damage than cars, but how much more? According to a GAO study, Excessive Truck Weight: An Expensive Burden We Can No Longer Afford, road damage from one 18-wheeler is equivalent to 9600 cars (p.23 of study, p.36 of PDF)."
http://archive.gao.gov/f0302/109884.pdf
http://facweb.knowlton.ohio-state.edu/pviton/courses2/crp776...
With regards to your point to taxes, remove the per-milage tax and charge a flat per-vehicle rate based on vehicle class, distributing the cost to trucks more than to passenger vehicles.