A new battle is beginning in Manassas, 150 years after its bloodiest one.

A parkway planned for the edge of Manassas National Battlefield Park would sully the area's historic character, environmental and historic preservation groups say, even though planners argue the road is needed to alleviate crushing traffic congestion through the middle of the park.

The Virginia Department of Transportation is ironing out an agreement with the National Park Service, or NPS, to build a 10-mile Tri-County Parkway along the edge of the battlefield to connect the city of Manassas with Interstate 66 and the Loudoun County Parkway near Washington Dulles International Airport.

But that would mean sacrificing history to big-dollar development, critics say, adding that the state doesn't seem willing to live up to earlier promises to close other park roads to through-traffic if it builds the parkway.

"The battlefield mess could be the worst of all worlds -- a new highway on the western end of the battlefield and no closure of the roads through the other side," said Stewart Schwartz, executive director of the Coalition for Smarter Growth. Schwartz thinks the parkway is the first link in an "Outer Beltway." "We think it's a very bad deal. It sacrifices our history."

The Battle of Second Manassas was fought 150 years ago this week. Confederate troops under Gen. Robert E. Lee routed a Union army commanded by Maj. Gen. John Pope. More than 22,000 soldiers were killed, wounded or missing as a result of the fighting.

The National Trust for Historic Preservation and the National Parks Conservation Association, along with two environmental groups, have also lined up to fight the parkway.

But supporters say the road will eliminate traffic congestion in the middle of the park, helping preserve the battlefield's historic identity.

"Manassas Battlefield is overwhelmed by traffic.The only way to preserve the historic integrity of this hallowed ground is to divert that traffic around the battlefield by building a bypass," said Virginia Secretary of Transportation Sean Connaughton.

Park Superintendent Ed Clark said the NPS is still in discussions with VDOT about the parkway and will decide to sign the agreement for the parkway only if the state can find a way to do more good than harm.

"Visitors today are extremely frustrated, many of whom fail to complete their planned tour of the battlefield just because they grow tired of sitting in traffic," he said. "We have the idea that if VDOT can build that road in such a way that would result in a net benefit to the park, then we're exploring the idea that that road could go forward."