People have been trying to film Jack Kerouac’s “On the Road,” the talismanic Beat novel, just about since the day it was published in 1957. “Heart Beat,” the 1980 semi-biopic, with John Heard as Kerouac; Nick Nolte as his madman muse, Neal Cassady; and Sissy Spacek as Cassady’s second wife, Carolyn, captured a little of the reckless spirit caroming around the room, grabbing from Kerouac’s lush, lunatic teletype-roll tome and from Carolyn Cassady’s memoirs. And there have been other imitators and aspirants.

But here, finally, and kind of anticlimactically, comes a real “On the Road,” directed by Walter Salles — who made “The Motorcycle Diaries,” inspired by Che Guevara’s prerevolutionary rambles in South America.

Cut to North America, where the ramblers are Sam Riley as Sal Paradise, Kerouac’s alter ego, and Garrett Hedlund as Dean Moriarty (alias Neal Cassady). Crisscrossing the States, dropping down to New Orleans from New York and then over to San Francisco and all around, the wild and crazy guys lob a lot of highfalutin gab about freedom and truth, the nature of man and the search for God. And then they smoke some weed, play some jazz, have some sex (mostly, but not exclusively, with women), and scrounge for cash.

If there’s an element of posturing and posing in the book — the eager Sal practically taking notes at Dean Moriarty’s feet — it’s even more pronounced in the film. Riley and Hedlund are handsome dudes and earnest actors, but to watch them here is to see two men not quite certain how to burrow deep into the characters they’re playing, because the characters they’re playing were faking it, too. How do you get to the core of someone who is still figuring out who he (or she) is, scratching for clues from the people who impress them, glomming onto intellectual and artistic theories that ring true?

“On the Road” is shot beautifully, and Salles has managed to find a two-lane America of small towns unblemished by strip malls, of big cities that still feel like they have room to breathe. Kristen Stewart drops her sulky “Twilight” shtick long enough to be convincing as the wild, teenage Marylou (based on Cassady’s wife, LuAnne), a sexually accommodating traveling companion with a sad, self-protective edge. And Kirsten Dunst gets the strongest — and least fun — scenes as Camile (aka Carolyn), Moriarty’s next missus, and the mother of his babies, stuck in her San Francisco apartment while the guys hit the town.

“On the Road” is an honorable homage to the bennies-and-booze-and-bebop-driven hegiras undertaken by the fiercely dedicated anti-establishment duo. But in Salles, screenwriter Jose Rivera and company’s effort to get the details right, they only get so far; not quite far enough.