In the past, there has been several requests for a route to visit the lower 48 states in one trip. I have developed a route (based upon past experience of driving all the specific roads but not in one trip). It is a circular route that starts and ends at the same point. In my case, it is Western North Carolina. There is very little back-tracking (less than 10 miles-6 in getting to Maine and two in visiting Utah.) A person can start at any point on the route and end at the same point and have visited all 48 states. The mileage is 8934 miles and would take about 140 driving hours. I would not recommend this but it can be done.
It is too long to post here but if you want the route, just send me a private message and I will gladly send you a copy.