The Alaska Highway has been improved and portions have been rerouted since its completion in 1942. Originally built after Pearl Harbor so the military could supply and defend Alaska, the old winding gravel trail has now become a very nicely paved highway with shoulders, pullouts and verges.
There are still sections of the original trail that you can access, such as this one. It, too, has been paved, but it was still fun to explore. The old bridge is original but the wooden decking has been replaced recently and is quite stable.