Spurred on by customer demand and dramatic leaps in computer technology, roller coasters and other amusement park attractions are bigger, faster and louder than ever.

The latest coasters scream along at nearly 100 mph. Another popular attraction drops passengers in a free fall from heights comparable to a mid-size skyscraper. And in Ohio, one theme park is building the tallest coaster in the world -- one that would take riders 310 feet above the surface of the Earth.

But after four deaths this year on amusement park rides, many of those who love the new thrills are beginning to wonder if those thrills are safe.

Experts say the same technology that has improved the rides has led to major advances in rider safety, allowing computers and electronic switches to monitor speeds, locations and whether everyone is buckled in properly.

The measures are aimed at protecting people from a variety of mishaps and mistakes, industry representatives said, though little can be done to stop thrill seekers determined to thwart precautions, as may have been the case this week at Paramount's Kings Dominion in Virginia.

Timothy Fan, a 20-year-old college student from New York, rode the Shockwave roller coaster Monday night as it climbed 95 feet before plunging its standing riders through a steep vertical loop and a sideways spiral. As his train was slowing before reaching the station, investigators said, Fan wriggled free of the safety harness, then fell accidentally to his death.

"If I undo my seat belt and open the door of my car when it's going 70 miles per hour down the highway, you can just imagine the dangers I'd face," said Chance Hester, safety manager at Kings Dominion. "We instruct riders to follow the rules, but we can't make them follow the rules."

Yet with the number of injuries in amusement parks nearly doubling in the past five years, some experts say too many modern rides depend on riders to ensure their own safety. Recent accidents have prompted legislators in California, Texas and other states to call for tougher regulation of amusement parks.

"The public is expecting more and more and more, and the park operators are giving them more and more and more," said William Avery, a veteran safety manager who runs an Orlando consulting firm. "That's okay to do that. But when you reach the point that personal safety relies on participation from the rider, then you've probably gone too far. We may have reached that point."

None of which means that coasters and other rides are particularly dangerous. Officials with the International Association of Amusement Parks and Attractions, based in Alexandria, like to point out that the country's 300 million annual parkgoers are more likely to injure themselves watching television, using a garden hose or driving to the theme park.

Kent Ladd knows all this, but he still likes to be careful. The Bel Air man checks out roller coasters by watching how much the cars shake and to what extent passengers can move around in their seats. Only then will he let his 10-year-old daughter aboard. He personally doesn't ride coasters that loop.

"You take more of a risk riding down the highway," said Ladd, waiting for his daughter and wife to get off the Two-Face coaster at Six Flags America in Largo. "You think about what can happen like everyone else. But every day you make a decision and take a risk, and that's the thrill of the ride."

Manufacturers, designers and safety experts say modern amusement rides are built to avoid nearly all foreseeable problems. Industry studies show that about 80 percent of all injuries are the result of rider error.

Jerry Aldrich, an Orlando amusement safety consultant, said the restraints on many newer rides include a microchip sensor that tells the operator whether the safety bars are latched. The computer controlling the ride won't allow it to proceed until all of the restraints are locked in place, he said.

"The casual mistake won't result in a problem," said Aldrich, who worked for Disney Corp. for 27 years. "You have to want to get around it. . . . I can't think of any rides that could not be gotten out of if you really wanted to do it."

Hester said the Shockwave's hydraulic lock system, which operates the safety harnesses, is designed to allow for almost complete failure of the harnesses while keeping riders locked into the trains. He said that even if a major component of the harness ceased to function, redundancy in the safety system would keep riders out of danger.

At least one organization believes such measures go too far. Bill Linkenheimer, president of the Kansas-based American Coaster Enthusiasts, said all the safety bars, seat dividers and other precautions are detracting from the thrill of riding coasters.

"A lot of it is overkill," Linkenheimer said. "We have to face restraint systems that are far less comfortable because they're trying to make them idiot-proof."

But accidents still happen through no fault of the rider. A 12-year-old boy plunged to his death Monday from a free fall ride at Paramount's Great America after the safety harness apparently failed. Later in the week, dozens of passengers were trapped -- some nearly upside down -- for almost four hours in 100-degree heat at a California park.

Kings Dominion officials reopened the Shockwave on Thursday after two days. At Six Flags in Largo, a white-water raft ride and a free fall drop attraction remained closed yesterday because of two accidents on similar rides elsewhere.

The federal government does not regulate established amusement parks like Kings Dominion, overseeing only the mobile rides used by traveling carnivals and the like. It's up to states and, in Virginia, localities to inspect theme parks and rides.

According to the U.S. Consumer Product Safety Commission, the number of accidents at amusement parks rose from 2,400 to 4,500 in the five years ending in 1998. The numbers refer to incidents at permanent amusement parks, rather than traveling carnivals. There were 43 deaths between 1987 and July of this year; 28 of those were at permanent parks. Ten deaths were on roller coasters.

Some of the statistical increase may be due to improved reporting.

None of that fazed Mike Stulginsky and his friends, who were seeking some final summer fun at Kings Dominion on Thursday before school reopens. Stulginsky, 17, of Herndon, watched as the Shockwave's trains navigated the ride's final 40 mph turn, where Fan was killed.

"Truly, I think roller coasters are really safe, and I think I'm going to be forced to ride this one," he said, laughing.

After his first ride, Stulginsky ran around to the entrance for a second attempt: "Good ride, good ride. I'm definitely going back on!"

Staff writers Jackie Spinner and Josh White contributed to this report.