your unsourced numbers for roads are wrong and at best representative of a rural area single lane mile not a 4 lane highway. Here are some better numbers for different places and types of roads:

https://www.fhwa.dot.gov/policy/23cpr/appendixa.cfm (scroll down a little ways)

so your reference for freeway is likely using a single lane number not the actual cost of a 4 lane high way which would be 12 - 80 million per mile.