>They don’t replace nearly enough cars and SUV’s to make up for the difference in fourth power of axle weight

A modest bus holds 40-50 people. Most commuter traffic is single driver, single vehicle. I don't know to which power the difference in axle weight would have to be to surpass the efficiency gains of replacing 40 to 50 American sized SUVs with a city bus, but I suspect it's more than four.