Tom Linzey of the Community Environmental Legal Defense Fund, which is representing the Whites, contends the Supreme Court doesn't have jurisdiction to "hear an appeal of an appeal."
The Whites had appealed the department's decision not to seek a review by the board, and the Department of Transportation appealed to the Supreme Court after the Commonwealth Court ruling.
"The court really doesn't know one way or another, but it's allowing the parties to brief the issue," Linzey said Thursday.
The department's position is the interchange plan did not require review by the board because it is part of an existing road, according to department spokesman Greg Penny. The Whites claim the exit constitutes new road construction and requires review.
"We've continued to move ahead with the final design of the interchange," Penny said Thursday. Federal funding of $5 million for the highway demonstration project was first approved in 1987, but various challenges have delayed the project and its cost has more than doubled.
Penny and Linzey both said the legal process will take months.
"If the court rules favorably ... we're still probably close to a year away" from construction, Penny said.
"It could be a year before they actually hear it," Linzey said. He said both sides will have at least three months to submit briefs to the court.
If the court rules in favor of the Whites, Linzey said the department will have to seek approval from the Agricultural Lands Condemnation Board before construction can begin.
The interchange is designed to relieve traffic on U.S. 30 and would link Chambersburg's north end with Greene Township. The township has spent $800,000 in recent years on legal and consulting fees to stop the project.
In 1998, the Department of Transportation unveiled a new design, moving the interchange about 1,300 feet south of its original location. Linzey said the exit would effectively deny the Whites access to about half their farmland.