Before the Parks Highway was built in 1971, there wasn't a road direct between Anchorage and Fairbanks. The fact that there wasn't a road there is interesting, because it's not that the Parks Highway would have been difficult to build. I think that the other roads in the state mostly had industrial origins (such as a trail for gold miners). At any rate, from a tourist perspective, the Parks Highway is the most useful road in the state... it certainly seems to be the busiest!
You can see the former route to Denali National Park from Anchorage was a bit more circuitous.