The month of September is the ideal time to witness this gilded spectacle on a scenic drive, but you have to time it right: The color lasts only about a week in most places. It's difficult to predict when exactly the leaves will turn in any given location. The best strategy is select travel dates in advance, but not destinations. Then go wherever the color is. Here are a few road-tripping routes, sorted by region, that have become fall-color pilgrimages for aspen lovers.