Not sure that this has been addressed in this discussion, but the fact that Michigan allows a gross vehicle weight of up to 164,000 lbs (in excess of every other state iirc) is a huge incentive for trucking companies to avail themselves of Michigan's roadways. And it stands to reason that it would encourage trucking versus rail in terms of shipping goods across the state (along with geography - as you suggest, Michigan isn't centrally located in terms of rail versus states like Ohio or Indiana, who fall squarely between Chicago and the East Coast).
The caveat on truck weights is that axle load requirements (which are used in calculating ESALs, which are the measurement used in designing asphalt/concrete pavements) are somewhat lower in Michigan compared to most states, which means that while the gross consist weight is higher, how the load is distributed across each chassis does result in lower point loads at axle locations. But still, while axle load requirements may be a little lower, that will still be counteracted if trucks pass over a roadway more frequently than in other states.
I don't have any data in front of me, but have a civil engineering background and some experience with pavement design. Policies on things like weights allowed on each axle (along with the type of pavement used, thicknesses, subgrade preparation/drainage, weather factors, etc.) can make a big difference on the service life of any pavement system.