After years of frustration, Linda and Michael Willie thought they had finally found a way to care for their handicapped daughter. Seven-year-old Kristen would spend weekends at home in Prince William County, then on Monday mornings her parents would drop her off at a special boarding school in Northwest Washington.

But soon they had another problem. Driving to and from Washington on Shirley Highway, they often sat in traffic for two hours -- time that did not pass easily for a child with a neurological disorder.

"It's terrible," said Linda Willie. "It's bumper-to-bumper. She's whining and complaining and there's nothing she can do."

To Willie, the solution seemed obvious: apply to the state for permission to use the car-pool lanes, which are restricted during rush hour to vehicles with four or more passengers.

Eight months later, the Willies still have not solved their problem.

Despite repeated appeals, Virginia transportation officials have ruled out a medical exemption that would allow the family to use the car-pool lanes with fewer than the minimum number of people.

To do so would hinder enforcement efforts and open the door to requests for exemptions of all types, officials said.

"When children have a serious illness, it's hard to say no," said Tom Farley, assistant district transportation engineer for Northern Virginia. "But in terms of providing blanket exceptions, we haven't been able to do that, and don't believe we should."

Commuter lanes have long been a subject of debate in Northern Virginia.

To supporters, they are a logical means of reducing traffic congestion without building new roads. To detractors, they are an unwarranted burden imposed by the government with little regard for individual needs.

"I'm in a very unique situation," said Willie, who has two other children and is an office manager at the Agriculture Department. "For the life of me, I can't understand what the big deal is."

Commuter lanes first became an issue with the Willies last fall, when they enrolled their daughter at the Episcopal Center for Children in Chevy Chase.

Public school had not worked out for Kristen. Stricken with viral encephalitis as an infant, she suffered from a range of neurological problems that made her all but unmanageable at home. She could barely hold a pencil or tie her shoes; frustration developed into temper tantrums.

"She was, literally, pulling out her own hair," her mother said. "She was trying to survive in a world that did not understand her."

The Episcopal Center seemed like the perfect solution. Kristen could spend weekends with her family, and during the week she would receive the special tutoring and therapy she required. "I felt really good about it," Linda Willie said.

Ordinarily, Linda Willie travels in a van pool from her home in Woodbridge to her job downtown. Michael Willie, a turbine mechanic for Potomac Electric Power Co., works an early shift in Maryland and usually avoids the traffic.

But Kristen's schedule requires that her parents drive her in on Monday mornings and home on Friday evenings, times that neatly coincide with some of the worst rush-hour traffic the area has to offer. "She cannot stand all the noise, all the sitting around," her mother said.

Willie said the time spent in traffic has exacted a heavy toll on the entire family. Because they have to leave early on Monday, the Willies send their other children to a neighbor's home on Sunday evening to spend the night.

Linda Willie first checked with Virginia State Police to see if they would grant an exemption, but was told they did so only in medical emergencies. She asked the Red Cross in Prince William County if it could provide transportation, but was told no such service was available. She considered hiring a taxi, but it was too expensive.

In October, after Kristen had been in school for a month, Willie wrote to Farley, seeking an exemption from the car-pool restrictions. "We are not afraid to make sacrifices," she wrote. "But {we} feel that if some leniency could be given, it would lessen the long day and hardship it presents."

Farley was sympathetic but firm. "The language of the law precludes granting exemptions to the HOV restrictions," he wrote back. "Only in the most serious of medical situations involving young children who are terminally ill and require special treatment to sustain life are special accommodations provided with the state police."

Farley said that to grant the Willies' request "would make it difficult to deny similar transportation needs to others, and ultimately jeopardize the courtesies provided to terminally ill children."

The state routinely receives requests from individuals and groups seeking exemptions from the car-pool rules. Motorcyclists, veterans, firefighters, off-duty police officers and members of Congress have requested exemptions, according to the Virginia Van Pool Association.

In an interview, Farley said he has heard from kidney patients who make regular trips into the city for dialysis, and has logged a few inquiries about whether dogs can be counted as people. "Some people in car pools are blind and they feel their seeing-eye dog should be counted as a person," he said.

Farley acknowledged that the Willies' case poses a special problem. He said he raised the possibility of a medical exemption program with his superiors, but they decided it would be too difficult to manage.

"We have not been able to find a way to permit special use of these lanes without creating substantial confusion or making enforcement of the regulations next to impossible," wrote Virginia Transportation Secretary Vivian E. Watts in a letter to the Willies. "I am sorry that I cannot provide you a more positive response."

Someone suggested that the Willies advertise for a fourth rider, but Linda Willie ruled that out. "I've got enough to do without worrying about a car pool," she said. "And what if he doesn't show up?"

Willie has not given up her campaign to win an exemption. She has written Virginia legislators, and she said she was recently told by an aide to Rep. Stan Parris (R-Va.) to be more "innovative."

"Is Mr. Parris suggesting that we purchase a helicopter?" she asked.