I know a civil engineer with now 15 years experience who has designed major road projects in the region...

He says they don't even calculate for cars, because they don't matter. Its the 100 ton trucks that matter. They are so heavy they actually make literal "waves" in the ground as they compress the earth under them at speed. Sure its less a wave and more a vibration, but they do move the earth under them with the pressure.

So the huge problem is trying to design roads that can accommodate the flex of the 100 ton trucks without shattering.

Of course the bigger problem is the fact we are moving bulk materials long distances on the roads via truck which is just not ideal. The problem is the rail networks in America haven't been expanded since the 1960's, if anything they shrank as lines were abandoned. We should have massively expanded the freight-rail networks for city-to-city hauling of everything but light goods, and have lighter 20-40 ton trucks do final miles delivery. This would GREATLY ease the stress on road infrastructure which we as a nation waste endless $billions rebuilding roads that cannot handle 100 ton truck traffic. And for installations that need high volume heavy delivery like factories, they should have their own rail attachments. Rail being flexible steel has NONE of the problems that gravel, asphalt, and concrete roads have with accommodating impressively heavy things.