If Interstate 270 southbound is jammed up, and it usually is, Scott Runkles takes U.S. 15 across the Potomac River and into Virginia, where he catches Route 7 and follows it, through all of that road's peculiar, inexplicable backups, to his office in McLean.

About 90 minutes. On a good day. And then 90 minutes to get home in the evenings.

On a bad day, Runkles, 32, can sit in his dark blue 1997 Jetta for nearly two hours, slogging his way through Montgomery County and then Fairfax County, or Fairfax and then Montgomery, before finally reaching his destination, which in the evening means home, in Jefferson.

All things considered, though, Runkles said he wouldn't have it any other way. Every work day, he crosses one state line and at least one county line -- sometimes two -- to get to his job as the manager of an accounting section for the mortgage lender Freddie Mac because his family's roots are in Frederick County.

With a growing family, housing is also a consideration, said Runkles, who has two children, ages 4 and 1.

"Moving down [to Virginia] right now is out of the question because my income would have to double in order to afford it," he said.

Like a growing number of Washington area residents, Runkles passes through several jurisdictions on his way to work each morning, and has found the length of his commute stretching each year as the region's roads continue to clog with long-distance commuters.

Figures released last month by the U.S. Census Bureau show that for the first time, a majority of Washington area commuters work outside the jurisdiction where they live. For many counties, the trend has meant a decline in the number of people who work near where they live -- a trend that is trouble to regional planners.

But despite the growing mobility across the region, Runkles remains the exception to the rule in his home county of Frederick, as well as Montgomery. Both counties managed to keep the number of "out-commuters" at virtually the same level between 1990 and 2000, according to census figures.

Montgomery actually experienced a small increase in the percentage of workers who remain in the county for their jobs: 58.6 percent of residents worked in the county in 1990, while 58.7 worked in Montgomery in 2000.

At the same time, the robust job market in Fairfax County -- fueled in part by the technology boom, which tapered off as the 2000 Census data were being collected -- drew an increasing number of Montgomery residents through the 1990s.

In 1990, 16,100 Montgomery residents, or 3.8 percent of the county's workforce, commuted to jobs in Fairfax. By 2000, that number had grown to 22,148 -- 4.9 percent of Montgomery workers.

"If this were a report card, I would say, yeah, we're doing pretty well," said Drew Dedrick, chief of research for Montgomery's planning department. Retaining residents who would otherwise travel out of the county for work, Dedrick said, "is no simple task, given this tremendous pull toward exurbia, toward expanding the region."

Many other counties in the Washington region experienced drops in the percentage of residents who remain in their home counties for work. Prince George's, for example, had a drop of one percentage point, from 40.3 percent of county workers staying in the county in 1990 to 39.2 percent in 2000.

In contrast, Fairfax County experienced a sizable increase in the number of workers staying in the county for their jobs: from 49.7 percent in 1990 to 52.7 percent in 2000.

Frederick County, which experienced tremendous job growth through the 1990s as the county's population grew, had a slight drop in the number of workers whose jobs do not take them outside the county.

In 1990, census figures show, 60.2 percent of Frederick County residents worked in the county; by 2000, that figure dropped to 58.9 percent.

"We're creating a lot of jobs here, some of which are being filled by existing residents and some of which are being filled by an increasing number of people coming into the county from other counties," said Jim Shaw, interim director of planning for Frederick County.

As Frederick County's population jumped from 150,000 to 195,000 in the 1990s, the number of jobs increased apace. In fact, despite a building moratorium in the city of Frederick and an overall slowdown of growth across the county, more jobs were created in Frederick than in any of Maryland's 23 other counties, according to figures released recently by the Maryland Department of Labor.

A 2002 study by that department showed that 2,846 new jobs were created in Frederick between 2001 and 2002. The next-highest were Montgomery and Carroll counties, with 2,161 new jobs each.

The increase not only has attracted county residents, Shaw said, but also has drawn residents from counties in western Maryland and Pennsylvania, who are often willing to work for less.

Like most counties around Washington, Frederick and Montgomery experienced increases in the percentage of people commuting from other places. Perhaps more telling, the diversity of locations from which those "in-commuters" arrive expanded significantly -- a reflection of the area's greater mobility.

"More people are willing to stay in place and commute to their new jobs than to move with jobs, because of the friction of changing place of residence," said Jeff Zyontz, chief of countywide planning for Montgomery County.

In Montgomery, the percentage of people commuting from distant counties increased almost across the board. Anne Arundel, Calvert and Arlington counties, for example, all sent a higher percentage of residents to Montgomery in 2000 than in 1990.

In Frederick, there have been sharp increases from Pennsylvania, West Virginia and Western Maryland, Shaw said.

As the distance commuters travel increases, their flexibility tends to decrease; it becomes more difficult to coordinate carpools or modes of transportation, such as taking a bus then the Metro, for example.

Runkles, the Jefferson-to-McLean commuter, tried carpooling for the first two years he worked in McLean. But as his responsibilities increased, so did his hours.

"It was becoming an inconvenience to the person I was carpooling with," Runkles said. "We would be scheduled to leave at four, and I might have to work until six or seven."

So Runkles started driving alone. The number of single-occupancy vehicles increased in most Washington metropolitan jurisdictions between 1990 and 2000.

In Montgomery, which prides itself on having an accessible and affordable mass-transit network, the number of commuters who drive alone increased 8 percent -- the same as the average for all the inner suburbs of Washington. Among those inner suburbs, Fairfax County had the highest increase in single-occupancy commuters, with 13 percent, and Prince George's had the lowest, with no increase at all.

The number of commuters who drive alone increased 38 percent, from 59,000 to 81,100, in Frederick County. Among all of Washington's outer suburbs, the number of single-occupancy vehicle commuters increased by 42 percent. Loudoun experienced the greatest increase, with a 93 percent leap in commuters who drive alone.

As job centers such as Frederick, Montgomery and Fairfax continue to produce new jobs, they draw people from farther away. A parallel trend is that people are willing to move farther away from where they work because, Zyontz said, "you always find cheaper housing further out."

In planner parlance, the effect is called a "traditional transportation gravity model," which means, roughly, that areas with high concentrations of jobs will attract people from a wider area than places without jobs -- the greater concentration of jobs, the wider the area employees will be drawn from.

The more an area develops, the higher home prices tend to go -- thus encouraging some people to move farther away from their work. As the District was built out in the middle of the 20th century, people moved to Montgomery, though they may have kept working in the District. As Montgomery became developed, people moved to Frederick. Now, Frederick is finding that workers are driving as much as 45 minutes to an hour, from other states, to work in the county.

"This is a very simple game," Zyontz said. "If Montgomery County wants to see what its problems will be in the future, we need to look at the District of Columbia. If Frederick County wants to see what its problems will be in the future, it should look at Montgomery County. That is the name of the game in an expanding region."

Scott Runkles, 32, commutes from his Frederick County home in Jefferson to Fairfax County. His workday commute takes about 90 minutes each way -- on a good day.Runkles waits in gridlock during his commute to Virginia from Frederick County. Census figures show that for the first time, a majority of Washington area commuters work outside the jurisdiction where they live.Runkles passes through several jurisdictions on his way to work, and has found the length of his commute stretching each year.Long-distance commuter Scott Runkles lives in Jefferson because his roots are in Frederick County. But high housing costs in Virginia are a consideration, too, said Runkles, who has two children, ages 4 and 1.