While it may not be the fastest road trip movie ever made, The Straight Story directed by David Lynch is still an excellent movie and I recommend you give it a watch if you haven't already. The movie which features the late Richard Farnsworth is based on the real life story of Alvin Striaght who drove his lawn mover from Laurens, Iowa to Mount Zion, Wisconsin so he could visit his ailing brother:
Because of health issues Alvin was unable to drive and he did not want to take the bus, so instead he decided to drive his lawn mower for a trip that took a total of six weeks. As I said above it's an excellent movie with a great story and interesting characters, which is something that all good road trip movies have so check it out.
Have a great weekend ~ Jim