That fourth-power is more complicated then your summary suggests. For example, it's also a function of road design, which is why a high-speed limited access ro

That fourth-power is more complicated then your summary suggests. For example, it's also a function of road design, which is why a high-speed limited access road is able to handle significantly higher loads than a suburban cul-de-sac. Consider that a bus weighs a lot more than a car, so a simple 4th power analysis suggests it will cause several orders of more damage than if everyone drove their own car. However, busses tend to run on bigger roads which are better designed to handle the weight (with the expectation that people will walk a few blocks to get to the stop), rather than residential streets which are mostly designed for private vehicles and the occasional delivery truck/van. On those roads, heavy passenger cars are relevant to road damage.