Riding around America on an endless road trip, to a hip hop soundtrack with plenty of sex, drugs and partying may sound like fun – and it is, in parts.

For the exuberant mag-crew of a white transit van, their task is to sell magazines in any way they can, living by their wits to achieve a sale, adapting their lines and persona to the neighbourhoods they are dropped off in, by their hard-faced, hard-assed, sexually predatory leader Krystal (Riley Keough), who takes most of their earnings at the end of the day, and instigates punishment of the loser with the least to hand over.

Based on a 2007 article in the New York Times on the brutality of mag-crew conditions, award-winning director Andrea Arnold, along with long-standing collaborator cinematographer Rob Ryan and sound recordist Rahad Omar crammed themselves into the dog box of a van which drove 12,000 miles across America for 56 days.

It's an observational movie, and its cast is made up of Arnold's characteristic blend of experience and first-timers. While Keough (Mad Max) and Jake, her chief salesman Shia LaBeouf (Transformers) are both film veterans, the rest of the cast are not.

Sasha Lane's mesmerising performance as Star, a new crew member recruited by LaBeouf holds your attention throughout – even as the landscapes blur and the days roll on – and seats flip up around you as cinema goers can stand no more driving, or need a comfort stop.

Lane was a last minute replacement, found sunbathing during spring break on a Florida beach two weeks before filming started; others were found in homeless shelters, outside the resort town of Panama City twerking and hip-hopping in a car park, or on the streets.

One hostel manager described them as the 'throwaways of America' – but not to Arnold. A largely amateur cast 'never give you the same thing twice'. Star's compassion and affinity for the natural world sees beauty in the most unappealing of settings. Star's spirit and honesty elicit unexpected restraint in those she meets.

"I wanted to find people whose lights hadn't gone off – where despite their hard starts in life, you could still see their potential, their beauty, and their spirit, and see they're not throwaways at all. I guess on some level, if the film is trying to show anything, it's that, " Arnold has said.

She succeeds, but don't try to get off the bus too early. There's nowhere to go.