After a decade of changes that included the building of I-66, the widening of Rte. 1 and the completion of the Metro system through Arlington, county officials are about to address once more the changes needed to make transportation easier for Arlington residents and commuters.

It has been a decade since the county updated its master transportation plan, the blueprint that affects everything from commuting on the county's 376 miles of roads to Sunday bike rides alongside the Potomac.

Though Arlington officials like to review their master plan every five years, court battles about I-66 and Rte. 1 and the developments wrought by Metro meant delay.

Up for scrutiny again this year -- in addition to improvements to many neighborhood streets and high-rise development corridors -- are projects such as making Rte. 50 a limited access highway, extending N. Quincy Street from Wilson Boulevard through what is now the Ballston Metrobus garage to Glebe Road, and building a bridge over Four-Mile Run from S. Eads Street to Commonwealth Avenue in Alexandria.

The update, expected to be finished by the end of the year, is traditionally a controversial process that affects not only Arlington residents, but hundreds of thousands of other Northern Virginians who work in the county or commute through it on their way to or from the District.

"Getting to and from work and to and from where you want to shop or take the kids to school is probably the single greatest determinant of how people view the quality of life in a community in which they want to live," said County Board Chairman John G. Milliken.

While trying to make transportation easier for residents, he said, "We also want a system which minimizes other people trying to get where they want to go in front of residents' homes . . . . The number one priority, in my view, is a transportation plan which primarily serves the people who are living here."

One way to minimize the impact of traffic on residential streets, county officials continue to preach, is to encourage people to use mass transit. Mark Kellogg, supervisor of the county's public works planning section, said only about 30 percent of the county's residents use mass transit, far short of the projected 40 to 50 percent.

"If we get the projected transit usage and a few highway improvements, we should be able to contain the levels of congestion to what we have today," Kellogg said. "If the transit usage doesn't materialize, it's going to be tough."

Many commuters now pass through Arlington on I-66 -- a highway that didn't exist in 1975 and that some had little hope would be built -- and will soon drive on a wider Rte. 1 through Crystal City. Both roads were the targets of prolonged court battles during a markedly virulent antihighway era when Arlington's personal property tax on cars was frequently raised to discourage their use.

Some of the antiroad sentiment still exists. But since 1975, thousands of newcomers have swarmed to high-rise residential and office buildings, making new demands on the local street system.

"The best transportation system we had was at the turn of the century, when we had extremely dense cities and people had to walk," said Henry S. Hulme Jr., the county's director of public works. "But the paradox is that people moved out to the suburbs because they don't like density and the social adversities that come with density."

The county, Hulme said, has tried to keep pace with development that has brought new residents, workers and more commuters. "In general, we've been able to do a creditable job of keeping up, but not as good a job as we'd like," he said.

Many of the projects that will be the focus of this year's update have been on the books for years but haven't been implemented for financial or other reasons. There undoubtedly will be lobbying for and against their removal from the master plan this year, Hulme said. They are incorporated in the plan as a safeguard, a planning tool that puts developers on notice that the county may build or widen a road through an area.

Some of the projects involve county roads while others target state roads that the county, under an unusual agreement with the state, will pay to improve with matching funds. One such project is the widening of Glebe Road from I-66 to Rte. 50, the county's major north-south access road and what Hulme describes as the county's "most critical" need. Widening has already begun at Glebe's intersection with Wilson Boulevard because the area is the gateway to the Rosslyn-Ballston high-rise corridor, an area that is expected to experience the county's most explosive growth in the coming decade.

Not everything in the master transportation plan review will involve roads. Other issues to be tackled are walkways, jogging and biking trails and mass transit, Kellogg said