LOS ANGELES — To make “On the Road,” director Walter Salles and star Garrett Hedlund had to go on the road.

Based on the classic novel by Jack Kerouac that inspired generations of young people to leave their homes and find their own paths, a lot of the film involved tooling around the country in a 4,500-pound 1949 Hudson.

Principal photography was in Montreal, San Francisco, Louisiana and Mexico from August to December 2010. Then Salles and Hedlund and a film crew started traveling the blue highways of America.

“We took only back roads and shied away from cities where the architecture had been homogenized, says Salles, who earlier made another try-to-find-yourself road movie with “The Motorcycle Diaries.” “We did this for two and a half weeks. We didn’t have a deadline and didn’t know where we were going to sleep at night.”

Bringing “On the Road” to the screen was a long haul itself.

Francis Ford Coppola has owned the movie rights for around 30 years but for one reason or another could not get the film made. There were screenplays by novelists Barry Gifford, Russell Banks and one by Coppola’s son Roman. But studios also wanted established stars to play Dean Moriarty and Sal Paradise (Neal Cassady and Jack Kerouac in real life), and Coppola wanted unknowns.

Then after the success of 2004’s “Motorcycle Diaries,” Coppola felt he found the right combination to make “On the Road” in Brazilian director Salles and screenwriter Jose Rivera, who had received an Oscar nomination for the film about Cuban revolutionary Che Guevara’s young days.

In 2007, though, Salles zeroed in on Hedlund as Dean and Kristen Stewart for the key role of Marylou, Dean’s child bride.

Both were relatively little known at the time. The pre-“Twilight” Stewart was coming off an eye-catching performance in “Into the Wild,” while the now 28-year-old Hedlund had made his screen debut in “Troy,” as cousin to Brad Pitt’s Achilles. Since then he has drawn praise as a soulful singer-songwriter in “Country Strong” and starred in “Tron: Legacy.”

Despite the delays in making “Road,” both actors remained committed to the project because the novel had meant so much to them when they read it as teens.

Stewart — who, of course, is a whole lot more bankable now — says reading Kerouac’s work “kick-started something” in her when she encountered it at 14.

Hedlund was 17 when he read it in high school. He says reading hadn’t been one of his favorite things growing up, but the novel, which was published in 1957 during the era of the Beat Generation, really impacted him.

“Seeing somebody who completely paved their own path when format was being shoved down your throat and seeing somebody who cut the cuffs with a spontaneous prose kind of changed the way I looked at literature,” says Hedlund.

In fact, the novel inspired the actor to compose his own “non-editing writing with no hesitation.”