Suggest you drive for approximately two hour intervals -- walking for 30 minutes between driving segments. Plan your stops so that you can pull into a town for your walk -- more interesting. I have done this for a number of years due to a medical condition that prevents siting for extended time periods. You will find that you feel better and will stay alert. If you fold these stops into meals, restroom stops, coffee stops, etc., it will be a more efficient use of time.