To get the essence of Sam Shepard, you have to hit the road.

Not metaphorically. Do it for real.

You ought to drive for a while and then pull off the highway, wait for a break in the traffic — if it's the right kind of road, the wait won't be long — vacate your vehicle and kneel down and slap the asphalt.

That's right. Give it a good, hard smack. Note how it's composed of nicks and ridges and tiny fissures. Feel the grit and menace of an American highway. Let your hand linger, and you might pick up the faint vibration of a distant car or the faraway tremor of a truck or two. Everybody's making some kind of getaway.

You'll sympathize with Wesley, a character in Shepard's 1978 play "Curse of the Starving Class," who says, "I could feel this country close like it was part of my bones." Or with the narrator in " Wisconsin Wilderness," a story in Shepard's latest collection, "Day Out of Days" (2010), who spends his nights "staring deep into the broad valley, eyes tracing the snaking car lights along US 66."

Highways are the nation's skeletal system, branching and probing, heading everywhere at once. Thus if you want to understand Shepard and his work — he's haunted by roads, the ones we take and the ones we don't — you can start by pressing your palm for a few seconds against a dirty berm.

Shepard, who will receive the 2010 Chicago Tribune Literary Prize for lifetime achievement at 10 a.m. Saturday at Symphony Center, is a startlingly unique figure in American cultural life. He's a Pulitzer Prize-winning playwright, a movie star, a musician, a screenwriter, a director, a poet.

But it's hard to imagine Shepard, who turned 67 Friday, enjoying either experience. Mostly, it seems, he drives. And thinks. And writes. And gives us a portrait of ourselves and of contemporary life that initiates a cringe and a shudder but not much of a contrary argument. Born in Fort Sheridan and raised mainly in California, he's often pigeonholed as a chronicler of the American West — but his true territory is the nation itself. It's a place, he seems to believe, that has failed to live up to its own potent mythology, betrayed its grand ideals.

"He makes us think about what it means to be an American," says Ann C. Hall, a professor at Ohio Dominican University who has written about and taught Shepard's work for many years. "Like David Mamet, he really pushes the limits of language — what is said and what is not said.

"He came on the scene and took American theater to another level," she adds. Indeed, in the mid-1960s Shepard swooped down onto New York's off-off-Broadway stage "like a tornado," Hall says, and he blew the doors off the place, turning out play after play after play with an angry passion that left audiences shaken but exhilarated.

Shepard has written some 45 plays, but between the late 1970s and the mid-'80s he wrote the four that are the cornerstone of his achievement: "Curse of the Starving Class," "Buried Child," "True West" and "A Lie of the Mind." They're about violent families burning with shameful secrets, about battling lovers, about shattered lives. They're written with a savage, earthy poetry that sounds not like poetry, but like the way people really talk; Shepard's dialogue is a kind of vicious vernacular. A lot of his work is about losers on life's margins, about drifters and misfits and alcoholics, and the twisted roads down which they ramble.

No wonder it appeals so much to Terry Kinney, co-founder of Chicago's Steppenwolf Theatre. Kinney starred as Tilden in a 1996 revival of Shepard's "Buried Child" (1978), a production that originated in Chicago and then moved to New York.

"All of his people are outsiders," Kinney says. "They can be very feral. Steppenwolf is very much in tune with the outsider. We empathize with people on the periphery."

And then there are the movie roles. Shepard specializes in straight-grained, lean-jawed characters such as test pilot Chuck Yeager in "The Right Stuff" (1983) or the farmer in "Days of Heaven" (1978) — watchful, laconic men defined by action, not talk.

In the short stories in "Day Out of Days," many of which are set in the Midwest, Shepard shows "his feel for the roll and pitch of landscape," notes Donna Seaman, associate editor of Booklist. "His characters are at once helpless in the grip of sorrow and free in their rogue solitude."

The tales in "Day Out of Days" read like notes from the road, scribbled on napkins from truck stops. They have titles such as "Dawson, Minnesota (Highway 212 East)" and "Indianapolis (Highway 74)." As Shepard writes in one, "After two runny eggs and processed ham, I hit the road by 7:00. It's hovering at around nineteen degrees. … Just barely tap the brakes and the whole rear end slides out from underneath you."

The only way to get a grip, it seems, is to keep on going, even if you don't know how or where it's all going to end.