Three bluegrass bands board a train in Oakland headed for New Orleans. It sounds like the beginning of a logic problem from a grade school math test, but it's really the beginning of 'Big Easy Express,' a documentary film starring Mumford & Sons, Edward Sharpe and the Magnetic Zeros and the Old Crow Medicine Show.

The bands in question didn't just board the train, either: they were the only passengers on the train, and they were vintage rail cars at that, as a nod to the 1970 Vintage Express tour that inspired them. Mumford & Sons used the tour as an opportunity to road test some new material, though its inclusion on the band's sophomore album has yet to be determined. The song, 'Where Are You Now,' is fitting since the it's is a kindred spirit of sorts to Steve Goodman's 'City of New Orleans,' bringing the the whole "trains to Louisiana" theme full circle.

Mumford & Sons lead singer Marcus Mumford has compared the film to "going back in time," but after watching the trailer for the film, there is one adjective that wouldn't leave our heads: stinky.

About halfway through the clip, someone, presumably a member of Old Crow Medicine Show considering the context, talks about how "All those little things make us kindred spirits." And then he explains just what that means. "Even the Mumfords are pretty grimy. They have grease and mustard stains on their pants, just like us. The Edward Sharpe guys haven't showered, probably, just as long as I haven't showered." This is the point where Nelson Muntz would say, "Smell ya later."

'Big Easy Express' director Emmet Malloy premiered the film at Austin's SXSW last week to rapturous applause, with a follow-up show on the University of Texas campus (their marching band plays a small role in the film). As an added bonus, members of the three bands reunited to play a set after the screenings, which featured even more new Mumford material. Below is a link to 'Where Are You Now.' Take a listen and let us know what you think in the comment section.

Watch Mumford & Songs 'Where Are You Now'