RICHMOND, JULY 16 -- Rebuffing Northern Virginia politicians, the Commonwealth Transportation Board approved final plans today for $392 million in improvements to Rte. 28 through Fairfax and Loudoun counties that do not include provisions for a rail line.

Local officials, chief among them Fairfax County Board of Supervisors Chairman John F. Herrity, have made repeated pleas for some form of rail service along the heavily traveled corridor near Dulles International Airport. But highway officials said yesterday that the right of way is not wide enough to accommodate a rail line in addition to the planned improvements.

"There's no room for it," said Jack Hodge, chief engineer for the Virginia Department of Transportation. "There's no way you can get off a train without stepping in front of a car."

The plans approved yesterday call for widening Rte. 28, also known as Sully Road, first to six lanes and eventually to eight lanes for 14 miles between Rte. 7 and I-66, with 14 new interchanges. The project is deemed vital to Northern Virginia's transportation network because of rapid development along Rte. 28, now a two-lane road that is among the most congested in the region.

In other action yesterday, the board approved the final design of the proposed Springfield Bypass, removing the last major bureaucratic hurdle from the path of the 33-mile road through Fairfax County.

"It is a big, big project," Hodge told the board, expressing satisfaction that the design of the long-awaited road had finally been approved. He acknowledged that the road would not please everyone, noting that some residents had wanted a high-speed parkway with fewer traffic lights and intersections. The approved bypass will have 35 traffic signals, about one per mile.

Hodge also said that the $242 million project does not include money for landscaping with trees and shrubs.

With its $392 million price, the Rte. 28 project is the most expensive being planned for Northern Virginia. Funding for that project hangs on the fate of the proposed Rte. 28 transportation tax district, which would assess commercial landowners along the corridor with additional property taxes.

Developers have yet to reach agreement with the state on how much they should contribute under the tax district. In an interview this week, Transportation Commissioner Ray Pethtel said he expects an accord by the fall.