Soon, smoke is billowing from engines, rubber tires are shredded down to steel wheels that screech and squeal as the competitors squeeze every last breath out of their dying machines. Sparks fly in all directions as torn-off steel scratches pavement and the odor of burnt rubber and God-knows-what burning under the hoods fills the lungs.

The demolition derby is back in town.

Demolition derbies have been a staple at American racetracks and county fairs since at least World War II - and remain hugely popular to this day. An estimated 3,000 to 5,000 are held every summer, according to Tory Schutte, founder of the Wisconsin-based Demolition Derby Drivers Association.

But derbies are constantly confronted with new challenges. They occasionally turn dangerous, as evidenced by a fireball that engulfed a driver at Riverhead Raceway in July, and drivers are increasingly being forced to compete with newer, smaller cars as the behemoths from the 1970s and '80s that make ideal derby vehicles slowly disappear.

The criterion for crowning a demolition-derby champion, however, has not changed: Be the last driver of a vehicle that can still move.

The temptation to smash a vehicle to smithereens is universal, derby drivers insist: Just ask anyone who has ever been stuck in a traffic jam or behind someone going 30 m.p.h. in the fast lane.

"Most kids get yelled at for wrecking a car. I can go out and have a ball doing it and I don't get in trouble for it," said James White Jr., who at 19 is among the youngest competitors at Riverhead.

Schutte is a self-appointed expert on "demos." His research finds they likely started in the late 1930s and early 1940s somewhere in the Midwest.

The first major exposure for demolition derby came in the early 1960s, when Jim McKay would televise from Islip Speedway on Long Island on ABC's Wide World of Sports.

"ABC helped bring in thousands of people," says Marty Himes, a racing historian who runs a modest museum in Bay Shore on Long Island.

Schutte, who claims to represent 25,000 drivers and runs the Wecrash.com Web site, says he has been pushing to standardize derby rules. But with no official sanctioning body, that has been a chore.

Basically, all derby vehicles must have a protective cage around the driver. Batteries and gas tanks are often moved inside the passenger compartment, making them less likely to be ignited into fireballs by the sparks that fly during crashes. Doors are usually welded shut and bumpers are taken off.

The combination of rising scrap-metal prices and the popularity of derbies has made it more difficult each year for competitors to find suitable junkers to use in competition. Riverhead and other tracks offer contests in various categories, including school buses and 8-cylinder and 4-cylinder cars. Track promoters buy school buses at a discount after the vehicles are deemed no longer safe for schoolchildren.

"Tell me it's not every kid's dream to come out and see that school bus that takes you to that rotten school be destroyed," Bob Rommeney says.

In the 1970s, Rommeney used to drive from his home in Queens to compete in Islip, but now makes the 140-mile round trip with his sons farther east to Riverhead Raceway nearly every weekend, where his eldest, 30-year-old Mike, is the defending demolition-derby champion. Younger son Kevin is beginning to race in some of the NASCAR-type competitions that precede the derby.

"You get it in your blood," says Bob Rommeney, who helps his sons build their cars. "You see your father doing something and you want to learn it."

Mike Rommeney, who has been competing for nearly 14 years, says there is a strategy behind the chaos.

"People think it's easy to go out and wreck a car," he said. "You've got to hit somebody every 60 seconds. But you don't have to hit that person at 60 m.p.h. You hit him 20, 10 miles an hour, but don't hit him with a solid shot.

"Hit him on his fender. Let somebody else destroy their car on that guy, and you wait until the end, then you've got a perfect car, they're halfway dead, and then you kill him."