After 11 years with the Virginia Department of Transportation's safety service patrol, Mike Karbonski can only shake his head at some of the things he sees that have dropped off vehicles on Northern Virginia's highways.

One recent afternoon, a garbage truck heading south on Shirley Highway spilled cardboard across the right two lanes, prompting Karbonski to call in a front loader to clean it up before rush hour. A few weeks earlier, a fallen L-shaped angle iron caused flat tires on six vehicles near Telegraph Road and Route 1 (Richmond Highway). The day after that, a mattress fell off a vehicle at the Capital Beltway and Interstate 66, striking a car and bursting into flames.

"The guy ran over the mattress, and it hung underneath," Karbonski said. "The catalytic converter and the muffler caught the mattress on fire."

Karbonski's supervisor, Chris Landis, said such road debris from cars and trucks "causes mayhem. If traffic is heavy, people are usually driving a little closer to each other than they should be, and a car in front of you will suddenly swerve out of the way [to avoid the debris]. Suddenly there is something in front of you, and you have to swerve out of the way. If there is someone on either side of you, it's an accident."

Cargo or vehicle parts that accidentally fall off cars and trucks are an increasing hazard on Northern Virginia's crowded roadways, according to traffic safety officials. Though most such debris is from passenger vehicles, the materials that drop from trucks often are the most visible to motorists. Nearly 16 years after the state began requiring trucks to cover their loads, many still spill gravel, sand, trash and building materials onto area roadways, sometimes with frightening consequences.

Stuart Roy's friends often introduce him as 'the guy who almost got killed by a flying pitchfork.' Last November, Roy was heading east on the Woodrow Wilson Bridge in a sport-utility vehicle when a pitchfork from a westbound dump truck hurtled through the SUV's windshield, stopping inches from Roy's chest. The pitchfork now is mounted on wood and displayed on a wall in Roy's Alexandria home, a reminder of his close call.

About 25,000 crashes and 90 deaths a year are caused by vehicle parts or cargo that are unintentionally discharged onto roadways in the United States and Canada, according to a report released in June by the AAA Foundation for Traffic Safety. Many of those accidents are preventable, foundation officials said, because they are the result of poorly maintained tires.

"Blown tires, tire treads, drive shafts, bumpers, hoods, leaf springs, and brake parts have all contributed to serious crashes," said the report, which did not have local statistics. "At highway speeds, even small debris can be deadly. Items such as hand tools, spare tires, tarps, and tie-down straps can pose a serious danger if they land on a congested highway."

Safety specialists said they fear the problem is getting worse in the Washington region, especially in growing areas such as Fairfax and Loudoun counties, where intense construction activity is underway to build the homes, schools, shopping centers, roads and other structures needed to serve an expanding population.

The mammoth projects to untangle the Springfield Mixing Bowl and replace the Woodrow Wilson Bridge involve hundreds of construction vehicles, some of which do not completely secure their loads.

Cruising along the Beltway one recent evening during rush hour, VDOT road safety patrolman David Bennett pointed out a dump truck to a reporter. A large mound of dirt was visible above the truck's cargo area, and a tarp covering the load was fluttering loosely.

"He doesn't have it covered properly," Bennett said, continuing with this possible scenario: "A big chunk of dirt comes out, somebody is following too close, it hits their windshield, they swerve not knowing what happened and hit somebody else."

Trucks carrying materials such as gravel and dirt must be covered by a secured tarp, according to state law, or face fines ranging from $30 to $500. Leslie L. Byrne, a former Democratic state senator from Fairfax who sponsored the covered trucks measure when she was in office, said for the most part the law has reduced the amount of litter on state roads.

However, she said, "There has been spotty enforcement. The condition of a lot of these tarps is problematic. Some of them have such gaping holes in them that [the drivers] might as well not use them." She added, "The commercial vehicles that carry garbage, construction debris and landscaping debris -- that's the mainstay of the problem."

Officials at the Alexandria-based American Trucking Associations said truck drivers are heavily regulated, while there are no similar rules for covering passenger vehicle loads. Bill Gause, an engineering specialist for the associations, said most of the hazardous material in roadways is from cars, light trucks and other vehicles, not heavy trucks.

Associations spokesman Mike Russell said, "It's comical standing outside Home Depot and watching how people [load their vehicles]."

Chris Landis of VDOT's safety patrol -- the people who assist motorists on state roadways and also help clean up vehicle debris -- said crews have picked up fallen desks, couches and a filing cabinet full of papers. During the summer travel season, safety specialists said, highways sometimes are littered with coolers, luggage, aluminum chairs and other vacation items that are not adequately tied down. Then there are the ubiquitous mattresses, many of which slide off cars after drivers and passengers mistakenly believe they can stick an arm out the window and hold the bedding on the roof.

"Or maybe with one little string holding it," Landis said. "Forget it. And when those mattresses go, when you are doing 65 mph, they kind of go airborne for a minute and flip a couple times."

Four years ago yesterday, a cooking grill fell out of a pickup truck, setting off a five-car pileup that killed one person, critically injured another and shut down northbound Interstate 95 near Fredericksburg for three hours.

Tractor-trailers that shed treads from poorly maintained and underinflated tires are among the worst offenders, Landis said.

In a spot inspection of 18 trucks on Aug. 20, the Loudoun County Sheriff's Office cited insufficient tire tread as one of the violations that led to half of the trucks being ordered off the road.

Trucking industry officials said the impression that trucks are more responsible for road debris likely stems from other mistaken perceptions people have about trucks. "The perception is definitely inaccurate," Russell said. "It's similar to the way they think of us in other areas: 'We are big, we are slow, we are always in their way.' " The trucking industry, he said, is "big and easy to kick."

The AAA Foundation's study, one of the few on the subject, noted that road debris-related crashes make up less than one percent of all crashes in the United States and Canada, although precise figures are difficult to obtain from law enforcement agencies.

"In our area, I think that it's more severe than the report would indicate," said Lon Anderson, spokesman for AAA Mid-Atlantic, basing his opinion largely on anecdotal evidence from phone calls and other communication with drivers.

The report also said that so-called secondary crashes from debris are probably a sizable figure, but that law enforcement officials do not always make the connection between the first crash caused by road litter and a second crash that occurs "upstream." Anderson explained: "You have a debris crash in one place, and a half a mile behind that you have secondary rear-end crashes. Is that because of debris? Well, yeah."

And even if the debris does not cause a crash, Anderson said, there are thousands of drivers a year who put up with flat tires, cracked windshields and other more minor incidents of vehicle damage from flying rocks and other materials that go unreported.

Karbonski said he once removed a large piece of a dump truck's tailgate from the Beltway that had damaged the tires and rims of five cars but caused no collisions.

The report praised safety crews such as VDOT's that generally detect and remove debris before it causes a serious problem. But the report recommended stronger enforcement, higher fines, better truck driver training and education campaigns for other drivers to reduce roadway debris.

Byrne said police should step up truck inspections. Landis said that VDOT should consider printing brochures that explain the dangers and consequences of carrying an unsecured load or driving on underinflated tires. Retailers of large consumer goods could distribute them at the time of sale, he said.

"Let the public know that it's not safe to carry a mattress on your roof," Landis said. "Maybe retailers could tell them up front that they could get a ticket: 'Unless you have a proper truck, don't even try to take it home.' "

Signs could be posted on interstate highways, Landis suggested, asking drivers, "Is your load secure? If not, you might get a ticket."

The report said that local governments should consider charging commercial trash haulers higher dumping fees if they arrive at landfills with improperly secured loads. Virginia is a leading importer of trash from other states, especially from New York, increasing the chances of trash blowing off trucks traveling through the Washington area on their way to landfills in southern Virginia.

Sgt. Wallace Bouldin, a spokesman for the Virginia State Police, said authorities enforce covered-load regulations at truck weigh stations or, for passenger vehicles, during routine patrols. The state also periodically has targeted enforcement actions similar to the Smooth Operator campaign, a cooperative effort between Virginia, Maryland and the District to reduce motor vehicle crashes resulting from aggressive driving. He urged drivers to call the state police on their cell phones at #77 if they see someone driving with an unsecured load.

James D. Coburn of Chantilly said he is more aware of road debris from vehicles since his first wife, Valerie Coburn, 34, was killed 11 years ago on the Beltway just west of the Wilson Bridge.

A 27-pound fragment of a worn metal brake drum dropped off a tractor-trailer and crashed through the windshield of the pickup truck in which she was riding. She died instantly in front of her husband, then 36, and their son, 8, and daughter, 6. The truck driver was fined, and the vehicle owners paid Coburn a settlement of nearly $1 million.

Coburn, who has remarried, said he still jumps when something as innocuous as a piece of paper or an insect hits the windshield of a car in which he is traveling. Many drivers do not understand the importance of maintaining vehicle safety, he said.

"We are only sorry after the fact."

Safety service patrolmen from the Virginia Department of Transportation, above, shovel loose cardboard into a front loader after a garbage truck traveling south on Shirley Highway spilled part of its load, blocking the two right lanes. Below left, VDOT patrol supervisor Mike Karbonski prepares to set up traffic cones to deter drivers from cutting through a highway cleanup operation.Clockwise from left: Stuart Roy narrowly avoided injury when a pitchfork pierced his windshield while he was crossing the Woodrow Wilson Bridge last year; VDOT safety service patrolman David Bennett removes a fender liner from a ramp at Telegraph Road and the Capital Beltway; VDOT's Mike Karbonski arrives at the site of the cardboard spill.Keith McKeever of the state Department of Transportation, above, directs traffic around debris. Below, VDOT patrol supervisor Mike Karbonski works at the computer he uses to file daily reports.