It was difficult to come up with a clue for Gumball Rally that was short and didn't sound like a clue for Cannonball Run. Between Gumball, Cannonball, and Mad, Mad, Mad, Mad World, as ensemble road trip races, I chose the latter because 1. I've actually seen it, and 2. I could write the clue easier. Both were on my list but didn't make the final cut.
Fun quiz, and there are plenty for another quiz such as, Nebraska, Two for the Road, Around the World in 80 Days, It Happened One Night, Paper Moon, and the entire list of Bob Hope/Bing Crosby "Road" movies.
An elderly WWII veteran finds out that his estranged brother has had a stroke, drives from Iowa to Wisconsin to see him, on the only vehicle he can legally drive--a John Deere riding mower. ["The Straight Story"]