For proof of this just look at the Alaskan Highway. During World War 2 the Army built a 1,700 mile long highway from British Columbia to Alaska. There was zero infrastructure or existing routes along the way. Also they had to deal with mountains, permafrost, and all sorts of stuff using 1940s technology. Construction started in March 1942 and was completed in October of the same year. Or 7 months.
For comparison here in DFW they built an overpass between Hwy 820 and I-35W. No actual new roads, just a new overpass. It took them 7 fucking years.