After four years of study and $4 million, the favored route for a tri-county parkway -- a highway that would connect Loudoun, Fairfax and Prince William counties -- is unlikely to get the federal funding or approval it needs to be built as it is proposed, said Ken Wilkinson, project manager for the Virginia Department of Transportation study.

Wilkinson said that the U.S. Army Corps of Engineers looks for roads that cause the least amount of disturbance to the environment and that the route favored by 40 percent of the public -- as determined through e-mails, letters and surveys -- is not the best of the four under consideration.

Wilkinson explained the corps' views at a meeting of the Prince William Board of County Supervisors on Tuesday. Supervisors expressed frustration that the route appears to no longer be an option.

The route is known as the Comprehensive Plan Alternative because all three counties have placed similar routes in their land-use plans. It is also the most expensive option, at $548 million, and would wind 11.7 miles from Route 50 near Dulles International Airport through a bit of Fairfax County in Bull Run Regional Park and east of the Manassas National Battlefield Park, ending at the Route 234 bypass and Route 28 interchange in Prince William County.

In a June letter to the Federal Highway Administration, Nicholas L. Konchuba, chief of the Eastern Virginia Regulatory Section of the corps, wrote that building the road would require a permit from the corps because it would "involve impacts to waters of the United States, including wetlands." Because the path's potential impact on wetlands and streams is greater than the other routes', the corps probably would not issue a permit for construction, Konchuba concluded in the letter.

Wilkinson said there might be hope, noting that Route 288 around Richmond had similar obstacles but was constructed.