JIDDA, Saudi Arabia — The young men start gathering around midnight, on a broad strip of highway between the desert and the sea. By 1 a.m. there are hundreds of them, standing in clusters alongside their cars, glancing around uneasily for the police.

Then, with a scream of revving engines, it begins: a yellow Corvette and a red Mitsubishi go head to head, racing down the road at terrifying speeds, just inches apart. Shouts go up from the sidelines, and another pair of racers shoot down the road, and another.

This may be the most popular sport of Saudi youth, an obsessive, semilegal competition that dominates weekend nights here. It ranges from garden variety drag racing to “drifting,” an extremely dangerous practice in which drivers deliberately spin out and skid sideways at high speeds, sometimes killing themselves and spectators.

For Saudi Arabia’s vast and underemployed generation of young people, these reckless night battles are a kind of collective scream of frustration, a rare outlet for exuberance in an ultraconservative country where the sexes are rigorously segregated and most public entertainment is illegal. They are, almost literally, bored out of their minds.

“Why do they do it?” said Suhail Janoudi, a 27-year-old sales clerk who was watching the races from the roadside with a faint smile around 1:30 a.m. “Because they have nothing else to do. Because they are empty.”

Some young people, asked why they risked their lives this way, said it was because of “tufush,” a colloquial Arabic word for boredom whose meaning is said by some to derive from the gestures made by a drowning man. Drifting, which tends to attract poorer, more marginal men, has also been an unlikely nexus between homosexuality, crime and jihadism since it emerged 30 years ago. Homoerotic desire is a constant theme in Saudi songs and poems about drifting, and accomplished drifters are said to have their pick of the prettiest boys among the spectators. Drugs sometimes also play a role. But a number of drifters have also become Islamic militants, including Youssef al-Ayyeri, the founder of Al Qaeda in the Arabian Peninsula, who fought in Afghanistan and was killed by security forces in Saudi Arabia in 2003.

“The idea behind drifting is, the economy and society don’t need you,” said Pascal Ménoret, an anthropologist who did four years of field work in Riyadh, the capital, and is now teaching at Princeton and writing a book on Saudi youth culture. “They are mostly young Bedouins who recently moved to the city, and whose lives are marked by suffering and self-destructive behavior.”

But most racers are more like young men almost anywhere: restless, thrill-seeking and madly in love with cars.

“It’s implanted in you when you’re a kid, and it stays with you,” said Sulayman al-Shulukhi, 29, who races every weekend night here and has adopted a 1950s greaser look: slicked-back hair, polo shirt with the collar up, jeans and white shoes.

He proudly showed off the modifications he had made to his Subaru Impreza: a carbon fiber spoiler, an intake valve, a special ventilation system, a turbocharger. He then jumped in the car for a ride along one of the racing strips near King Road, not far from Jidda’s Red Sea coast.

“We get up to 120 kilometers per hour on this part” (about 75 miles per hour), he said, as he accelerated down a perilously short trip of highway, “and 200 on this next one.”

As he drove, Mr. Shulukhi narrated a tale of a recent accident on this road in which a friend’s car had caught on fire during a race, and another one in which a driver had spun out of control and died after his car burst into flames. His world is full of driving disasters and driving heroes, some of them local men. He frequently invokes the racing movies “The Fast and the Furious” and its sequels, and “Death Race.”

Later, when the roads have emptied out a bit, it is time for some drifting. Raif Mansour al-Dammas, a skinny 21-year-old who looks much younger, gets into his beat-up white 1980s Nissan and revs the engine until white smoke pours out. Admiring shouts go up from a cluster of young men.

Then the car leaps forward, accelerating furiously, and breaks into a sudden skid, spinning around, nearly colliding with a concrete barrier and leaving thick black marks on the pavement. A stifling smell of burnt rubber hangs in the air.

Standing nearby, Mr. Shulukhi explained that he and his friends, who all race Subarus, were not really drifters. The distinction is more about social status than activity; he and his friends are mostly middle class and do not see themselves as outlaws.

“That’s a different path from what we’re doing,” he said. “That’s crazy, forbidden stuff.”

Mr. Shulukhi mentions the famous case of Faisal al-Otaibi, 27, a drifter who was sentenced to death after his car crashed during a joy ride in 2005, killing three teenage boys he had taken along with him. The sentence was reduced this year to 3,000 lashes, 20 years in prison and a lifetime driving ban.

Since the arrest of Mr. Otaibi, who is always known in the Saudi press as Abu Kab (meaning, roughly, the guy with the baseball cap), the Saudi police have cracked down on drifting, treating all deaths that result from the practice as criminally negligent homicides.

But even drag racing is dangerous, and despite its prevalence in every major Saudi city, the police try to discourage it.

Just after 1:30, a group of police cars show up, lights flashing, sending the racers scattering. The officers do not arrest anyone. They just step out of their cars and begin talking to the young men in a paternal manner, urging them to go home.

“We have another place we go when this happens,” Mr. Shulukhi said confidently, getting into his Impreza and driving a few blocks to a shopping center parking lot. There, scores of other young men are waiting by their cars, some examining their engines. At 2:30, the police show up again, the next step in a game of cat and mouse that lasts much of the night.

This time Mr. Shulukhi and his friends drive north, stopping for coffee at a drive-through called French Roast, until they reach their ace in the hole: a dark strip of highway just outside the city with a construction site on one side and desert on the other. They drag-race their Subarus along a quarter-mile strip for another hour or so.

About 5 a.m., the road begins to fill up with delivery trucks driven by Pakistani immigrants, doing the kind of low-wage job most Saudi men refuse to take. The racers decide to call it a night, and drive reluctantly home.

Bryan Denton contributed reporting.