An amendment that would limit parking to 1,000 spaces at the Mark Center until new roads or an environmental study are completed was passed by the House of Representatives on Thursday.

The amendment, authored by Rep. James P. Moran Jr., is attached to the National Defense Authorization Act currently making its way through the House.

“This parking cap is critical to prevent a traffic nightmare that will be caused by full occupation of the Mark Center in the fall,” Moran said in a statement. “The alternative is unendurable delays on already overcrowded roads.”

The Mark Center, located at Interstate 395 and Seminary Road, will soon be the workplace of 6,400 federal employees, under the Defense Department’s Base Closure and Realignment, or BRAC, process. By law, the moves must be completed by Sept. 15.

The Defense Authorization bill also includes an option for Defense Secretary Robert Gates to delay moves at seven BRAC locations for up to one year. The Mark Center site is among those locations.

“The best remaining solution for Northern Virginia commuters, including those who will be transferred to the Mark Center, is to delay the move until all road fixes are in place,” Moran said in a statement. “A one year delay gets the ball rolling in the right direction and buys us more time to get this situation corrected.”

U.S. Army officials agreed to pay $20 million for short- and mid-term road improvements around the Alexandria location. That road work will be completed in two years. Virginia transportation officials have set aside $80 million and are in the midst of an environmental study for a HOV ramp from I-395 to Seminary Road.

The House is expected to vote on the full bill later Thursday. Then the Senate will consider it.