It used to be about $10k/mile for the hardest routes in the US - where they would have to literally widen t-junctions, increase bridge height clearance etc. I

It used to be about $10k/mile for the hardest routes in the US - where they would have to literally widen t-junctions, increase bridge height clearance etc. I also got most of my info back in the day by "Jerome A Paris" thread on Eurotribune - sadly that forums is no longer active now.