Jerry Cimino, founder and curator of The Beat Museum, delves into the saga that lead to finally getting Jack Kerouac's On The Road adapted to film. His article reveals that after shooting the film from August through December of 2010, director Walter Salles and star Garrett Hedlund went on the road together with the film's '48 Hudson and a crew of five in April 2011. No one else in the cast (which includes Viggo Mortensen, Kirsten Dunst, Steve Buscemi, Kristen Stewart, Amy Adams, Alice Braga and Elisabeth Moss) knew about this trip, part of Salles' "quest for authenticity." Here is an excerpt from the article and this photo, courtesy of HuffPost.
...unbeknownst to just about everyone he and Garrett Hedlund took to the road for a second time in April of 2011. They spent two weeks along with a crew of five and blasted 4,000 miles across the back roads of the USA. They purposefully avoided the interstate highways not built until the 1950s, retracing as best they could the original route of the two lane roads Jack & Neal drove. The purpose of this unpublicized trip was for Walter and Garrett to be involved in the "Second Unit" shooting themselves. True to their desire to make On The Road as authentic as they could they wanted to capture the images of the '49 Hudson roaring across the continent with the sights and sounds of the country in the background. The story of On The Road is also the story of America and the film makers wanted to capture the physical and human geography at the core of On The Road as part of the film.
Here's more about the '46 Hudson they drove and the speeding tickets they avoided.