Andrea Arnold is one of the best and most distinctive British writer-directors of her generation, and, until now, ‘British’ has been the operative word. As audacious as her films have been, her first two – Red Road and Fish Tank – sprang from the English tradition of kitchen-sink social realism, and her third was an adaptation of an English Lit classic, Wuthering Heights. Her new film, then, sounds like a major departure. As you might guess from its title, American Honey sees Arnold crossing the Atlantic. She has swapped council estates and Yorkshire moors for a the sunbaked Midwest.  What’s most atypical about it, though, isn’t its setting, but the fact that Arnold has left behind the tight plotting of her previous work. When British film-makers head to the US, they tend to embrace more commercial narrative structures, whereas Arnold has done the opposite, making a free-floating, semi-improvised travelogue which rolls along dreamily for two-and-three-quarter hours. It’s bracing for most of that time, but it eventually becomes as numbing as any long motorway journey. Some viewers will be asking, “Are we there yet?”  Some viewers will be asking, ‘Are we there yet?’  One ingredient which American Honey does have in common with Fish Tank is a teenage heroine who dreams of escaping her straitened existence. Star (striking newcomer Sasha Lane) is a dreadlocked 18-year-old who is first seen scavenging food past its sell by date from a skip so that she can feed two children. (Half-siblings? Stepchildren? Who knows.) Her world is so small that that she is immediately fascinated when a white minibus packed with a dozen wild youths pulls into a Kmart carpark. One of them, the cockily charismatic Jake (Shia Lebeouf), invites her to join them. They drive from town to town, he says, staying in motels, knocking on doors, and spinning hard-luck stories in an attempt to sell magazine subscriptions. Next stop, Kansas City. Attracted to this fast-talking rogue, and by the chance to change her fate, Star climbs aboard.  There is a moment when the pistol-packing Jake threatens to turn the film into a 21st-Century Bonnie & Clyde, and there are echoes, too, of Oliver Twist, with Jake as the Artful Dodger and the team’s sullen boss, Krystal (Riley Keough), as its bikini-clad Fagin. But in fact the crew’s entrepreneurial activities are more or less legal. Despite their gangster tattoos, play fights, genital flashing and questionable bodily hygiene, it turns out that they aren’t leading Star into a life of crime, and American Honey doesn’t become a thriller. In several scenes, its skimpily-dressed heroine jumps into a car or a truck owned by an older man, and we’re just waiting for him to assault her (or vice versa). But no: she always gets back in the minibus, unscathed. Bottles are opened, joints are lit, hip-hop is cranked up, and the crew drives onto the next town.  Inspired by a magazine article, American Honey feels like an artfully shot documentary about an America which is rarely shown in films, and where civilisation seems to be petering out. There is a sweet scene in which the minibus reaches the outskirts of Kansas City, and Star’s new friends gasp at the only skyscrapers they’ve ever seen. But they don’t ever visit a town centre, and, after the opening section, they don’t even venture into a restaurant or a bar. They never encounter the police or any other authority figures, either. As their travels take them past abattoirs and oil fields, there is less and less to distinguish human society from that of the insects and animals which Arnold includes at every opportunity.  American Honey is an exhilaratingly unconventional, unjudgemental ride. It has crisp images of towns which are either being built or falling apart. It depicts hormonal working-class Americans with a sweaty authenticity reminiscent of Larry Clark and Harmony Korine: 11 out of the 15 main cast-members had never acted before. It also benefits from a fearless central performance which suggests that Sasha Lane, having played Star, is about to become one. But are these virtues enough to sustain a 162-minute film? Even at the end of that time, very few of the characters have been differentiated from each other, and we don’t know much about Star that we hadn’t learnt an hour earlier. Her relationships with the tempestuous Jake and the hostile Krystal aren’t resolved, and you get the feeling that the gang might just keep roaming forever, without going anywhere. As admirable as the film is, it could have been better if Arnold had packed her talent for plots when she made her Atlantic crossing.  If you would like to comment on this story or anything else you have seen on BBC Culture, head over to our Facebook page or message us on Twitter.  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Andrea Arnold is a distinctively British film-maker – but for the first time she has made a picture in the US. How successful is the transition? Nicholas Barber in Cannes finds out.