"There will be portions of the road with no pavement or gravel, and there will be heavy machinery which obviously have limited visibility."
Mountain bikes can handle gravel, and heavy machinery operators with limited visibility need to have flaggers to avoid visibility issues with cars and motorcycles, not just bicycles. IMO, these two stated reasons from the newspaper report are not enough.
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury