Dozens of Prince William County residents capitalized on the appearance of a key player in the debate over the proposed Bi-County Parkway Tuesday to reiterate concerns about the contentious state-planned road.

The proposed 10-mile parkway would connect I-66 in Prince William County with Route 50 in Loudoun County, and is considered, state transportation planners say, to be a crucial section of a planned north-south corridor.

Because the state-proposed route of the road skirts Civil War ground at the Manassas National Battlefield, the National Park Service must sign off on the parkway. Battlefield Superintendent Ed W. Clark addressed the Prince William Board of County Supervisors on Tuesday, and his presence drew out opponents of the road.

Clark told supervisors that the park service’s top priority is “removing traffic from the park.” For the parkway to be built, Clark said, he must have assurances from the state and from Prince William County that Route 234 through the park would be closed.

Prince William supervisors have agreed that the 26,000 commuters who make their way through the park daily would need an alternative. County officials have said that a long-planned bypass around the park should be built if Route 234 is shut down.

Clark told supervisors that 75 percent of the funding for the $300 million bypass would be allocated by Congress and the rest paid for by the state.

No dollars have yet been allocated to the bypass, Clark said.

Many also use U.S. 29 through the park. Clark said that if the parkway is built, “traffic calming” measures would be used on that road so that no one speeds through the park. He said that he is not sure what those measures would be but that they would not involve speed bumps.

Supervisor Peter K. Candland (R-Gainesville), picking up on Clark’s notion that the best way to preserve the integrity of the Civil War park is to limit traffic through it, said he had another idea for preserving the park. The best way to prevent the ruin of a protected rural area, he said, is to prevent “building a four-lane road through it,” he said to applause.

Candland asked whether Clark worried about damaging the park’s relationship with the surrounding community, given the backlash against the road and Clark’s intention to support the parkway.

“We are interested in working with our local residents,” Clark said. “Having the conversation is so vitally important.”

Several residents said Clark and the park service have not been open about plans for the parkway. “Unfortunately, we have not had” a good dialogue with the park service, said Philomena Hefter, a Pageland Lane resident who opposes the road. The parkway would be built through and near Pageland properties, prompting a particularly strong backlash from that neighborhood.

Clark “should have let us know,” Hefter said. “We should have been participating in the discussion.”

Clark’s agency is one of four — VDOT, the Virginia Department of Historic Resources and the Federal Highway Administration are the others — that must sign off on the road before funding can be allocated. Clark said in an interview that he wants to ensure that the language in the final legal agreement, known as the Programmatic Agreement, is “unambiguous” in terms of assuring that Route 234 is shut down when the parkway is built.

The business communities in Prince William and Loudoun have supported the Bi-County Parkway, saying that it provides a chance to spark economic development and better connect two of the fastest-growing counties in the country. They also say that the connection would provide an additional cargo route to Dulles International Airport.

Page Snyder, a Pageland resident who has helped organize protests, said that opponents are planning similar demonstrations when Virginia Transportation Secretary Sean Connaughton is scheduled to appear before supervisors on Aug. 6.