CANNES – “The only people that interest me are the mad ones,” mumbles Sam Riley’s Sal Paradise on more than one occasion in “On the Road” — directly lifting, of course, one of the most quoted lines from Jack Kerouac’s insistently quotable novel of the same title. A one-time manifesto of sorts for independent living that railed against authority, capitalism and good old-fashioned punctuation in equal measure, the book has, for its pains, been appointed the bible for shiftless college students the world over, most of whom would claim to share Paradise’s (and, by extension, Kerouac’s) disdain for the the functional, the rational, the balanced. 

It’s hard not to wonder, then, what Paradise and Kerouac would have made of Walter Salles’s assiduous, attractive and somewhat airless adaptation of “On the Road,” none of the virtues of which — its methodical loyalty to the material, its meticulous visual construction, even its strategic demographic tailoring — come from the repertoire of the mad. Salles and his “Motorcycle Diaries” screenwriter Jose Rivera have fashioned a distinctly unspontaneous film from a text about going where the road takes you, a paean to madness that never once loses its mind.

That’s not to dismiss the risks that have been taken in realizing this project at all — a structurally elastic 140-minute film about driving, drifting and indiscriminate fucking is no “Twilight” sequel, even if it does star Kristin Stewart — but watching the finished result 44 years after executive producer Francis Ford Coppola first set the wheels of an adaptation in motion, you wonder if the outcome could ever have been worth the bother.

To their considerable credit, Salles and Rivera have politely — perhaps too politely — silenced the widely prevalent if largely unsupportable notion that this particular novel is “unfilmable”: here, before our very eyes, is something that sounds very much Kerouac and, ye gods, looks very much like a film too, with common rhythms and textures tying together both those obligations. Hollywood has, after all, inadvertently adapted “On the Road” for the screen countless times before, given how extensively Kerouac’s Beat philosophy has moulded the politics and structure of the classic American road movie: the adventure-seeking bikers of “Easy Rider” are really just Dean Moriartys with more fringe on their jackets, while the final-straw feminists of “Thelma and Louise” may be forced into their escape more than Dean and Sal, but are equally driven by an anti-domestic epiphany. 

Perhaps it’s the book’s general bleeding into any number of pop-culture avenues, then, that makes the final arrival of a straight adaptation feel so much less totemic than this faintly self-awed film purports to be: even if it weren’t quite as lacquered and anachronistically nostalgic as Salles’s involvement always suggested it would be, could it ever feel truly vital or dangerous? Between intervening revolutions like feminism, civil rights and simple rock-and-roll, much of what was once incendiary about Kerouac and his peers’ stance has passed into the accepted liberal ideal. That doesn’t make it irrelevant, but it does require closer contextual examination and contrast to spark it into rhetorical life.

Rivera’s faithful if judicious paring of the novel offers only teasing flashes of such thinking — most of them evident in its cheerful approach to sex. Its concern with the fluid sexuality of dimly yearning social malcontent Dean (Garrett Hedlund) feels particularly contemporary, frisky even, with the scarcely-concealed strain of homoerotic desire between him and Sal still a malleable point for contemporary audiences. It’s no surprise that the opaquely charismatic Dean powers the film more than Sal and his irksomely overdetermined narration (which some of us would argue Kerouac laid on a bit thick even in 1951), though that has at least something to do with the casting: the loose-limbed, heavy-lidded Hedlund may be working less hard than British actor Riley (here adopting the same flailing affectations and perma-sneer that scuppered his work in “Brighton Rock”), but his performance demonstrates a better ear for jazz.

The supporting cast is an asset: Viggo Mortensen repeats his recent party trick is livening up inert prestige fare with independent eccentricity, Kirsten Dunst provides some real unvarnished feeling as Dean’s forever-abandoned good girl and, yes, Kristen Stewart acquits herself well as his livewire child bride. Still, the enjoyable parade of famous faces suggests Salles himself is in need of distractions on this episodic trip; daunted by the freeform possibilities of Kerouac’s “purity of the road” celebration, he’s opted for something a little more pre-sliced.

The overarching chaos of Kerouac’s narrative, with its multiple unfinished trips splintering their participants a little more each time, registers merely as pedantic structural crowding here, its stops and starts too closely sequential for the characters’ building anguish to make itself felt. Without a hint of unruliness in Salles’s direction or even Eric Gautier’s exquisitely honeyed cinematography, watching other people’s freedom becomes about as unrewarding a practice as hearing about other people’s dreams. “On the Road” can be filmed, and faithfully at that; transferring Kerouac’s treasured madness to the screen may take another go or two.