Motorists trapped in some of the worst traffic in the country here in the Washington area must face a hard truth: Anywhere from a quarter to half of the congestion we suffer through is our own fault.

We run out of gas. We butt into merge lines. We slam into each other. When trouble strikes someone else, we slow down and gawk.

Traffic engineers call the ensuing backups "nonrecurring" congestion. They are the delays that madden people most, the kind that no amount of careful planning can control. They strike anywhere at any time, with the power to turn a barely tolerable -- but at least predictable -- drive into a full-blown mess.

The chronic backups on such roads as Interstates 66 and 270 stem from too many vehicles on too little pavement, experts say. Fixing those would require widening roads, increasing mass transit, changing development patterns and persuading people to drive less -- all things that have proved expensive, controversial and, worst of all, slow to bring relief.

But reducing the unpredictable backups that result from crashes and breakdowns, traffic experts say, would be one of the easiest and most affordable ways to make a noticeable and relatively speedy dent in the problem.

In short, experts say, motorists can do far more to help ease their own pain.

"We can do a better job of making the system somewhat less congested and certainly more reliable," said Tim Lomax, a research engineer at the Texas Transportation Institute who co-wrote the annual study that ranked Washington's traffic misery third worst in the country.

"If we can address the traveler behavior," Lomax said, "we have a chance of curing some of the problem."

Up to 60 percent of traffic delays stem from something other than too much volume, according to the Federal Highway Administration: 25 percent from crashes and disabled vehicles, 15 percent from bad weather, 10 percent from work zones, 5 percent from special events and 5 percent from poor signal timing. Lomax said pinpointing the various causes of congestion is extremely difficult. However, he said, the Texas study estimates that almost half of the Washington area's delays result from collisions and breakdowns.

While motorists cannot control the weather or road crews, traffic experts say they can control the sizable chunk of congestion caused by crashes and breakdowns simply by driving more carefully and taking better care of their vehicles.

In the Washington region, volume delays began to surpass congestion caused by incidents in 1995, according to Lomax's estimates.

Whereas incidents used to cause most delays, everyday bottlenecks now account for 53 percent.

But breakdowns and crashes cause the most disruptive backups because people cannot plan for them. Some traffic experts and police officials estimate that for every minute a lane on a major highway is closed or obstructed during rush hour, it can take up to five minutes to clear the traffic backlog. That adds up quickly.

Fairfax County police use a rough "mile-a-minute" estimate. For every minute a lane is closed, expect a mile of slowdowns. A lane on I-95 blocked for two hours can slow traffic as far north as Baltimore and as far south as Richmond, police say.

In the Washington region, such nonrecurring delays are so common, they have almost become recurring. During a typical morning rush period, police estimate that the area has more than 100 collisions affecting traffic.

Here and across the country, transportation departments pay strict attention to preventable congestion. In Los Angeles and San Jose, which vie with Washington for the title of Most Miserable Traffic, local governments are rolling out public education campaigns encouraging safe driving. If people would drive more carefully, California officials theorize, they would cause fewer collisions and save not only lives but time. Other jurisdictions have stepped up ways to clean up collisions -- and get traffic moving -- more quickly.

In the past decade, the Maryland State Highway Administration has doubled the number of roadside cameras, variable message signs that alert drivers to problems and roving emergency patrols that assist motorists who are broken down or in a crash. A University of Maryland study of the state's traffic operations center that monitors the cameras and dispatches emergency crews found the system saved motorists $527 million in time, fuel and decreased emissions in 2001. That was up from $378 million saved the previous year.

The Virginia Department of Transportation has wreckers patrolling the Woodrow Wilson and American Legion bridges. Ten safety crews patrol major highways looking for problems. In the coming weeks, a new radio station, 1620 AM, will announce major traffic incidents on I-95 and the Capital Beltway in the Springfield area. Maryland and Virginia are spending $36 million to make sure collisions and breakdowns do not cripple traffic during the massive rebuilding of the Wilson Bridge and the Mixing Bowl interchange.

Many incidents have become the stuff of legend, including one in which highly explosive powder was spilled at the Mixing Bowl or another when a man threatened to jump from the Wilson Bridge. But in an area as congested as the Washington region, it takes hardly anything major to delay traffic.

"When you've got a disabled vehicle in a lane for 30 minutes, that can cost you an entire rush hour by the time things get back to normal," said VDOT spokeswoman Joan Morris.

WTOP radio traffic reporter Bob Marbourg said he believes that the region's main traffic problems stem from roads carrying more vehicles than they were built to handle. Those chronic bottlenecks worsen accident-related congestion, he said, because the more closely vehicles are crammed together, the more likely they are to collide. The more traffic backs up after a first collision, he said, the more likely that motorists coming up on the slowdown or jockeying for position will cause other collisions and, in turn, more delays.

Marbourg, who has covered traffic in the region since 1979, said in the past 10 years transportation departments and police have become a "well-oiled machine" to quickly spot and clean up collisions. He said he cannot say the same of motorists.

Often the worst backups result from people slowing down to gawk at trouble. Marbourg said he notices "phantom delays," lasting long after an incident is cleared, from motorists rubbernecking at the spot where they think the incident was.

"It's a form of self-inflicted congestion, but it's human nature," Marbourg said.

A concerted effort to take turns merging would keep traffic flowing at 20 to 30 mph or more even in the worst places, Marbourg said, rather than traffic coming to a halt when a driver zooms ahead and then tries to nose in at the last minute.

"We don't do a good job of sharing the road," he said.

Traffic safety researchers say it is extremely difficult to change driver behavior. Case in point: Even with penalties and decades of public awareness campaigns, many motorists do not wear seat belts and drive drunk.

But even persuading people to take better care of their vehicles, and to make sure they have enough gas, would help. In Northern Virginia, three of four incidents handled by roving safety patrols are breakdowns or abandoned vehicles, according to the Virginia Department of Transportation.

Getting people to improve their driving habits would not solve the region's traffic woes, said Lomax, the Texas traffic researcher, but frustrated motorists should do their part.

Unlike many traffic problems, Lomax said, "these are things that are within people's ability to control."

Traffic backs up on Interstate 395 near Alexandria. Experts say up to 60 percent of traffic delays are caused by something other than too much volume.Bruce Barton, a supervisor with the Virginia Department of Transportation, helps a stranded traveler by repairing her flat tire on Interstate 395. Bruce Barton of the Virginia Department of Transportation talks on his cell phone while assisting a stranded traveler on Interstate 395.