vastly simpler to build the road up on pylons for a few miles.
1, build new road on pylons beside the old road for a few miles.
2 ,switch traffic to new road on pylons.
3 , rip up old road
4 , build some fences ,plant some grass and shrubs
5 ' repeat in each eco zone and local water shed and other areas where there are lots of critters....too chicken to cross the road