Yellowstone trip: Mammoth Hot Springs. I've never seen this hot springs with water in it--it dries up when there is a drought. The little town there is neat to walk around and there is usually elk laying around.
An NC State University student describes various ways to road trip in a sustainable style. Checking tire pressure reduces amount of gas used, turning off your car at stops instead of leaving it running, and picking up littler throughout your trip are some ways to go on a sustainable road trip. This article promotes sustainable tourism by car. The student author is unbiased towards road trips because they are providing factual examples and not just opinions about traveling by car.