"The only ones for me are the mad ones,'' runs Jack Kerouac's most famous sentence. ''The ones who are mad to live, mad to talk, mad to be saved, desirous of everything at the same time, the ones who never yawn or say a commonplace thing, but burn, burn, burn like fabulous yellow Roman candles exploding like spiders across the stars …''
If Jack Kerouac had never written On the Road, wrote Ray Manzarek of the Doors in his autobiography, ''the Doors would never have existed''. Perhaps a lot of other things wouldn't have existed, either, at least not quite as they subsequently did: new journalism, the counterculture, sex and drugs and rock'n'roll. No Charles Bukowski writing about his low-life high jinks, no Tom Wolfe hanging out with Ken Kesey and the Merry Pranksters, no Bruce Springsteen whooping that he was born to run. ''It changed my life,'' Bob Dylan wrote, ''like it changed everyone else's.''
On the Road is an account of five road trips between New York and San Francisco, up to Chicago and Denver and down to Mexico, taken by Kerouac - renamed Sal Paradise for fictional purposes - alone and with various friends in the late '40s, going to bars and pool halls and living in humpies with seasonal workers.
He wrote the first version in three weeks in 1951 on a continuous scroll of drawing paper, glued together and trimmed to fit the typewriter so he need never stop; Kerouac called his method ''spontaneous writing''. No publisher would have a bar of it. It took six more years, many rewrites and some intrusive editing by unknown hands at Viking before it came out in 1957.
The New York Times gave it a rave review. The long delay, moreover, ensured its appearance was timed impeccably; literary rebels were in the news. Two weeks earlier, the poem Howl by Kerouac's friend and mentor Allen Ginsberg had been the subject of a famous obscenity trial that was, at that moment, yet to be decided. In the tight atmosphere of Cold War America, these people were like an explosion of defiance. Kerouac, by nature a silent observer - ''the great rememberer'', Ginsberg called him - found himself the spokesman for what he had dubbed the Beat Generation.
''Beat'' meant poor, beaten down, scrabbling with the dregs; as so often with Kerouac, it was an expression he had absorbed in conversation, this time from a street hustler, junkie and sometime writer named Herbert Huncke, who told him one day, ''I'm beat to my socks.''
For Kerouac, it took on an additional meaning derived from ''beatific''; the road was part of a quest that was religious, his characters fiery angels. For everyone else, it summoned images of the bebop jazz that infuses his writing. Influential as they were, however, the Beats were less of a movement than a coterie of literary romantics, all of them disaffected or marginalised in some way: gay Allen Ginsberg, drug-addicted William Burroughs, Buddhist poet Gary Snyder and, above all, the thrillingly delinquent Neal Cassady, whose manic personality as the barely fictionalised Dean Moriarty propels On the Road in a rush of speed and words.
Part of the book's power was that, despite the pseudonyms Viking insisted Kerouac use, people knew it was mythologised truth: the drugs, the frenzied sexual adventures, the gleeful poverty, crazy all-night driving and all that passionate reading and writing really were taking place somewhere in what Kerouac called ''the holy American night''.
What ignited it, however, was the fire of language. Nobody else had written with such exuberance; the sentences raced across the page, despite being jammed with poetically babbling turns of phrase that often made no ostensible sense. The literary establishment hated it: its lack of discipline, its excess, its cast of ''sideshow freaks'' with their appalling ''outlaw'' values.
These academicians had no idea how much young readers, recoiling as Kerouac himself had done from the postwar promise of a prosperous life of respectable lawn-mowing, longed for the freakish and the outlawed. On the Road, opined The Village Voice, was ''a rallying cry for the elusive spirit of rebellion of these times''.
You would imagine a film would have quickly followed. In fact, Kerouac was offered $US20,000 for the rights, a tidy sum in the early '60s, but he refused it; there were about 10 attempts to bring it to the screen, including one by Francis Ford Coppola.
But they all collapsed, one way or another; the Brazilian director best known for The Motorcycle Diaries, Walter Salles, is the first to have managed it.
His On the Road, to be released in Australia next month, was unveiled at the Cannes Film Festival in May. Sam Riley, who played Ian Curtis in Control, plays Jack/Sal; Kristen Stewart of Twilight fame plays Marylou (her real name was Lu Anne Henderson), who was 15 when she married Dean; Kirsten Dunst plays Camille/Carolyn, Cassady's second wife and the author in real life of a memoir called Off the Road.
Cassady, the ''hero of the Western night'' who turns into Dean Moriarty, is played by a little-known actor called Garrett Hedlund, who took a bus for three days from Minnesota to audition, wrote about the trip and read what he wrote to Salles.
''It seemed like Neal Cassady was writing to us,'' Salles says. Salles was 18 when he read the book and fell in love with it.
''It was the opposite of what we were living in Brazil in 1977. We had a dictatorship. Everything was forbidden. Even inside families, life was very conservative and in this book it was the opposite. I read it many times after that.''
I was 17 when I read On the Road, just a couple of years before Salles found it. Did it change my life? It certainly gave voice to things I wanted, given I had thus far spent most of my time in school uniform staring at a square of sky above Elwood between bouts of homework. I can't remember how I knew about the Beat writers, but in those days, the mid-'70s, even fashion mags ran features on cool writers and artists.
The poet who ran City Lights bookshop in San Francisco and published Howl, Lawrence Ferlinghetti, certainly came to me that way; I also recall an interview with Ginsberg and his lover Peter Orlovsky, talking about being gay. That sounds ordinary now, but we still snickered about our lesbian teachers in the '70s. There was the sudden sense of a cultural world that existed outside ours but was there for the taking.
Young people always feel like that, of course, which is why On the Road is still a reading rite of passage. Stewart is 22; she read On the Road only eight years ago. Same thing.
''I was like, 'Wow, I've got to meet people like this; otherwise, I'm not going to be as cool as I could be, as smart as I could be, as challenged as I could be, you know what I mean?'' she says.
''I kind of identified with Sal's character: I've never been one to lead the way, but I wanted to surround myself with people I want to run after, people who kind of shock me.'' It became her first ''favourite book''. ''I didn't enjoy reading before that but I ripped through it. It … opened so many doors.''
The funny thing here is that On the Road is often assumed to be a primer for boys. That's certainly what its literary haters say - that it is ''mainly read by young men'', as if it were a book about cars for petrolheads. (Kerouac confesses he hated driving; Dean calls Sal ''fearful of the wheel''.) It is true, admittedly, that a teenage girl reading On the Road in the 1970s had to imagine herself a boy, like one of those brave, disreputable women pirates of an earlier era.
Women were, in fact, central to these men's lives - Kerouac lived with his mother, along with a succession of wives, until he died, at 47, of a massive internal haemorrhage caused by alcoholism - but they were peripheral to the myth they were making of themselves.
Worse, they were the brakes in a world where acceleration was everything.
At one point, Sal is thinking of marrying a virtually invisible character called Lucille.
''I want to marry a girl,'' he tells Dean and Marylou, ''so I can rest my soul with her till we both get old.'' A few pages later, however, he is reflecting morosely the hopelessness of it.
''She would never understand me because I like too many things and get all confused and hung-up running from one falling star to another till I drop. This is the night, what it does to you.''
For a woman to hit the road alone would have been unthinkable. There must be a fair number of girl readers who grew up to become feminists, not in order to be prime minister but because they wanted to do this, the crazy stuff.
In fact, the original scroll version of On the Road, which was finally published in 2007, included more about the female characters; Kerouac had stripped them out, at the publisher's instruction, to give the story focus. In his film, Salles says, he lets Sal and Dean drive off and stays with Camille as she struggles to support Dean's children.
''It shows that loneliness is painful and that she has a job; she is probably going to leave the baby with a neighbour and off she goes to work in a hospital,'' he says. ''Yes, this quest is memorable, to amplify all forms of freedom is memorable, but there are consequences.''
Not that these women were all doormats. Stewart met Lu Anne Henderson as preparation for playing Marylou. Unlike the men of her youth, she was thriving in her 80s. ''The difference between the two is that in the book she does seem quite used,'' Stewart says. ''But she is a bottomless pit, you can't waste her and she expects just as much in return; she is so f---ing generous.''
Salles saw Marylou as a real, if unacknowledged, adventurer. ''She makes the decisions to go or to stay and she doesn't have that Catholic sense of sin that is ingrained in Kerouac. She is an explorer just like Dean is an explorer.''
By the time On the Road was published, Kerouac was barely recognisable as Sal Paradise. At 35, drink and dysfunction had turned him into a filthy old bigot. He detested the hippies and yippies who claimed On the Road as inspiration and was loud in his support for the Vietnam War and McCarthy's communist witch hunt. McCarthy, he told an interviewer, had ''all the dope on the Jews and the fairies'' who apparently lived at the bottom of his brain's addled garden. Ginsberg, who was pretty much the poster boy for both these categories, was beatifically forgiving; asked in the interview I read whether Jack himself was ''a fairy'', he let his lover and fellow poet Orlovsky answer.
''In a tiny sense of the word,'' Orlovsky said. ''Perfect,'' Ginsberg said.
But for the wider world, it didn't matter how crackers Kerouac had become. He died in 1969; the mercurial Cassady had died of a combination of drink and drugs, aged 41, in the Mexican desert the previous year.
Like the readers who had pulled on torn Levis and headed out along the highway for themselves, On the Road had its own life by then.
It had left home, hitchhiked around the world via millions of bookshelves and was part of the lives of all the would-be writers and rebels who aspired to join the social movements Kerouac had so vituperatively disowned.
It is 55 years since the book was published. ''Nobody knows what's going to happen to anyone beyond the forlorn rags of growing old,'' Kerouac writes on the last page, as he watches the sun go down in ''the long, long skies over New Jersey'' and contemplates the vast bulk of land between the coasts.
As it turns out, the book that was about the man he loved, this ''most fantastic parking-lot attendant in the world'' full of ''a yea-saying overburst of American joy'', is a requiem. ''I think of Dean Moriarty, I even think of old Dean Moriarty the father we never found, I think of Dean Moriarty,'' he says finally.
As I write this, I touch the book on the desk and think of him, too.
On the Road opens September 27.