Traffic is seen during rush-hour headed westbound on Interstate 66 in Vienna in this August file photo. (Marvin Joseph/The Washington Post)

If it feels like you’re sharing the road with a lot more angry people these days, that’s because you probably are. The number of people who admit they feel “uncontrollable anger toward another driver” has doubled since 2005.

Twelve percent of the people surveyed in a Washington Post poll said they often feel such anger. That’s more than 1 in 10 drivers on the road. A less statistically perfect way to view it: If you’re zipping along in four lanes of Capital Beltway traffic, it’s a safe bet you’re in the company of several drivers who are in a volatile mood.

The number of younger drivers who said in the survey that they often feel road rage was roughly 1 in 6, or 18 percent.

It gets worse, according to Leon James, author of “Road Rage and Aggressive Driving: Steering Clear of Highway Warfare.”

That 12 percent of people who admit to frequent spikes of “uncontrollable anger” are being honest with themselves and the people who did the survey. Lots more people get just as angry, but they won’t own up to it, said James, a professor of psychology at the University of Hawaii. He likens “driving under impaired emotions” to driving drunk. “It’s a real danger, just like alcohol,” he said. “You just don’t make the right judgments, and you overlook reality.”

The truth about road rage

About 85 percent of the drivers James tests say they see aggressive driving around them, but only 30 percent admit to being aggressive themselves. “The anger triggers are built in and just about the same for everybody,” James said. “So when people say, ‘Who has road rage?’ I say, ‘Everybody.’ ”

Some people who feel empowered by the gas pedal flash to anger when another driver impinges on that sense of entitlement. Others who are intimidated by driving are upset when misbehavior by other drivers feels threatening. And drivers who aren’t feeling particularly powerful or frightened already are dealing with the stress of interaction at high speed with a group of unpredictable strangers.

It is a volatile combination that leads to angry gestures, blaring horns, crazy retaliatory driving and, sometimes, worse.

The latest local road rage incident to get public attention ended with the arrest of a detective from New Jersey on a charge of second-degree murder and manslaughter. There were conflicting accounts of what transpired, but a bout of anger that covered several miles of Anne Arundel County highway ended with Joseph L. Walker allegedly shooting Joseph D. Harvey Jr. to death.

In March, two drivers faced charges after a moving confrontation over a desired lane change on the Anacostia Freeway caused a female driver to wave a knife at a male driver, who responded by brandishing a handgun. (No one was hurt.)

Three years ago, a dump truck driver purposely rammed a car on Interstate 95 during rush hour, leading to charges in Prince William County. The car driver also faced charges for allegedly firing 13 shots at the truck. State police said that was the culmination of 20 minutes of reckless behavior by the two drivers that covered more than four miles .

And in 2007, a young couple on their way to the beach died after what police called “exchanging obscene gestures” on Interstate 270 with the driver of a green pickup truck. Police said the dispute ended when the truck driver slammed on his brakes with the other driver just behind him, forcing the car to swerve off the road, where it hit an embankment.

“Aggressive means you don’t care if you put others in danger, and that’s a personality flaw,” James said.

James said the capacity for anger behind the wheel is learned from the back seat, where children see grownups venting at traffic or other drivers.

“I call it ‘road rage nursery,’ ” he said. “Children learn that in a car, your personality becomes more violent, more angry, more foul. So by the time we start driving, we are mentally rigged for road rage.”

It’s subconscious, he says. “For example, if your lane is going faster than the lane next to you, you feel good and you relax. If it’s the other way, you tense and grip the wheel and become more stressed,” he said. “You think, ‘Wow, 50 cars just passed me, should I switch?’ ”

And what if you feel a driver cut you off on purpose? That’s what’s most likely to set someone off, said Christine Wickens of the Center for Addiction and Mental Health in Toronto, who authored three studies of aggressive driving. “It’s what we would call a near-miss,” she said. “It’s anxiety-provoking.”

Sometimes it causes more than anxiety. “People feel a need to retaliate,” James said.