From there, twin transmission lines will carry 500 kilovolts each to a new substation to be built in Kemptown, Md.
The twin lines, which likely will cut across southern Washington County, will be supported by 125-foot towers on a corridor that will be 400 feet wide in most places, Allegheny Power spokesman Todd Meyers said.
The $1.8 billion line is needed to prevent other power lines from becoming overloaded and to prevent blackouts projected as soon as 2012 as the demand for electricity increases, according to PJM Interconnection, a nonprofit agency that controls the electricity grid in 13 mid-Atlantic states and Washington, D.C.
PJM authorized the construction of the line in June 2007.
Allegheny Power and American Electric Power, which will share a portion of the 290 miles of lines, have begun studying potential routes and are accounting for cultural and historic places, wetlands, and endangered species and plants as they do so, Meyers said.
The companies plan to finish these studies and apply for regulatory approvals from the Maryland and West Virginia public service commissions by the end of this year.
Meyers said Wednesday that Allegheny Power will hold public meetings on the route before it applies for regulatory approvals but said dates and locations for those meetings have not been set.
The companies hope to finish building the line by 2012.
Some people have said the schedule could leave regulators hurrying to approve the line in an effort to keep the power companies from using a new federal law to bypass state approval.
Under a federal energy law passed in 2005, the federal government designated a "national interest electric transmission corridor" from northern Virginia to New York that includes part of the PATH line.
The law would allow power companies to bypass states and secure land through the federal government if their project is deemed vital to national energy interests.
In a meeting hosted by the Maryland Department of Natural Resources' Power Plant Research Program last week, state officials asked counties and local environmental and historical groups for information in advance of Allegheny Power's application to make sure the state does not inadvertently delay the approval process, Thompson said.
Washington County planners are compiling maps of historic places, rural legacy areas, preservation districts, National Park sites and other relevant places for the Maryland Public Service Commission.
"We will argue for the protection of historic areas and things like that. We may not have the final say on this, but we're going to make our presence known," Thompson said.
Antietam National Battlefield Superintendent John Howard said he is concerned that the power lines will be visible from the battlefield, which he said is known nationally for its uninterrupted viewshed.
"We don't believe they would consider putting the lines through the battlefield, but the question is will you be able to see it? When you come here, it's a very easy place to get lost in. There's not a lot of houses, factories or even monuments. It's a serene place," Howard said. "We don't want that to be destroyed by these power lines."
Washington County Commissioners President John F. Barr said he met Thursday with representatives from Allegheny Power who told him that there is a chance the line could run south of Washington County entirely.
He said the county commissioners have not taken a position on the PATH line but said "if it ends up having a serious impact here, we're certainly going to stand behind our citizens."