Sixty percent of the traffic in Fairfax County in the 1990s will be generated by cross-county trips made by those who live and work in the booming county, according to John F. Herrity, chairman of the Fairfax County Board of Supervisors.

Traffic patterns throughout Northern Virginia are changing dramatically, Herrity told a recent meeting of the Northern Virginia Builders Association.

Herrity was stumping familiar territory to drum up support for the county's November road bond referendum.

He said 45 percent of trips today are already cross-county and predicted major increases in trips inside Fairfax as its commercial and high-technology industry base continues to expand.

"Unless we are able to get people who work in the county moved around, businesses and industries are going to take another look," Herrity warned.

"You have good, selfish reasons to go out and vote for the bond issue. Take the message to your friends, neighbors and enemies if you agree with me" on the need for passage of the bond issue, Herrity told the builders.

He said funds from the bonds would help pay for major segments of the long-planned Springfield Bypass, which is designed to connect Route 7 in the western part of the county with the Route 1 corridor in southeastern Fairfax.

Herrity, other local political officials, Chamber of Commerce leaders, many citizen groups and business and development leaders generally consider the bypass vital to the county's future road system.

Not many years ago, Fairfax was primarily a bedroom community, supplying workers and executives for private industry or federal jobs in the District. That has changed.

"From the 1950s to now, money has been spent on getting people to the District," Herrity said. Money spent in the 1980s to get Fairfax residents to the District should be focused on funneling commuters to Metro subway stations that are open or slated to open next year, he said. Herrity emphasized the need for spending money on roads that crisscross the county.

Herrity was talking to representatives of an industry that is very aware of the transportation needs and costs of road improvements in the county. The board chairman said developers are large contributors to road improvements.

"In the past five or six years, developers have proffered promised more than $100 million" in new roads or improvements to existing roads," Herrity said. "The single largest contributor to road improvements has been the private sector."

Developers agreed to pay for those improvements as part of the rezoning of large tracts of land for major developments in almost all parts of Fairfax.

While the county's zoning process allowing builders to propose major road improvements has been criticized by some citizen activists, most builders say the success of their developments depends on good traffic access. They also say that the only way to finance those roads is for developers to pay for them.