Have you ever taken a Greyhound? Granted I have a n=1 experience, however a Bus leaving Denver (with a final destination of Dallas) leaved much to be desired.

The route-through method means that you'll stop about once every hour for 15~20 minutes for on-off and snacks/restroom. If you're still somewhat wakeful these stops are just at the twilight phase and you don't get truly restful sleep.