Until Friday morning, John Yannarell was a middle-aged engineer living a quiet life in a bucolic hilltop exurb in outer Montgomery County, as the single parent of a teenage daughter.

Now he faces criminal charges, including attempted murder, in a startling allegation of road rage directed at a seemingly random driver on Route 422 in early-morning traffic.

"None of us could imagine this," said Judy Rossi, a neighbor in Yannarell's tidy Gilbertsville subdivision.

A nondrinker, Yannarell, 50, blew off stress with a boat at the Shore and a little-trafficked Web site called "Pitch Your B - Online" that he founded to vent life's frustrations. He was president of his homeowner's association and generally known as a calm, patient man.

But then he faced early Friday traffic on his oft-clogged route and, according to police, something violently snapped.

Elizabeth Cox, 31, was driving east toward her job at an eye doctor's office when she called police at 7:15 a.m. to warn of an "erratic driver swerving in and out of traffic" behind her, police said. Near Mile Marker 186 in Upper Providence Township, she pulled into the right lane to let him pass.

Then the worrisome car, a silver 2008 Buick Lucerne, passed her on the right shoulder and the driver fired a gun at her, police say.

Cox first felt "a jolt or a bump and thought someone has sideswiped her," Trooper Denea L. Durham said.

But when Cox saw blood, she realized she had been shot - apparently by the middle-age white man she saw driving down the shoulder.

Cox pulled her black Ford Focus to the side of the road and called 911, providing details of the other vehicle - including a tag number that was promptly traced to Yannarell.

She was shot in a leg and elbow, but Durham said it was not clear whether one or two shots were fired. She was flown to the Hospital of the University of Pennsylvania, where she was treated.

"She's obviously very lucky that her injuries were not worse," said her attorney, Thomas A. Sprague. "She just cannot believe that this happened. I don't think anyone else can either."

As Cox was being treated, police were hunting for Yannarell, swarming the hillside neighborhood around his white two-story house.

When he surrendered to state police in a lawyer's office in Norristown at 12:50 p.m., police were also given a 9mm Smith & Wesson handgun registered to Yannarell. By then, his driving history was coming to light.

Court records show that Yannarell has been cited eight times since 2002 for disregarding traffic lights or stop signs in Montgomery, Delaware, or Chester Counties. He pleaded guilty in seven of the cases and was found guilty in the other. He was also cited for speeding in 2005 in Montgomery County.

Though he was a flawed driver, acquaintances said Yannarell displayed no warnings of a combustible demeanor. He lived a quiet, private life, and met the other residents of the Estates of Warwick subdivision mainly through the homeowners' association, where he served on the landscaping committee before becoming president.

"He keeps to himself," said Rossi, whose husband, Bob, is vice president of the residents' group. "There aren't a lot of people here who know John very well."

On his Web site, Yannarell was more extroverted, writing about his marital and dating difficulties, along with occasional rants about topics including Tiger Woods ("What a disappointment!") and President Obama ("This health care plan is scary!").

"I am very handy," he wrote in a self-description, "as I was a truck/diesel/fleet mechanic for 20 years and have owned my own home since age 21. I am looking to meet that special woman."

He was arraigned Friday night and bail was set at $500,000. A preliminary hearing was scheduled for Tuesday.

Contact staff writer Derrick Nunnally at 610-313-8212 or dnunnally@phillynews.com.