The proposed extension of the Metro rail lines in Northern Virginia: to Centreville on the Orange line, to Potomac Mills and Woodbridge on the Blue line, to Fort Belvoir on the Yellow line. (Google Maps/WMATA/Tom Jackman)

Northern Virginia’s growth shows no signs of slowing. So two congressmen from our area, Gerry Connolly and Jim Moran, have introduced the “Northern Virginia Metrorail Extension Act,” which would study extending the Orange line to Centreville, the Yellow line down Route 1 to Fort Belvoir, and the Blue line down I-95 to the Potomac Mills mall in Woodbridge.

“We have to start talking about choices and alternatives right now,” Connolly told me. “We may decide that light rail is better. Or bus rapid transit. But let’s have the debate now. That’s what’s been lacking.”

Moran pointed out in a release that “Northern Virginia has the worst traffic in the nation ... Public transit is the answer to this unrelenting congestion. It’s better for commuters, our economy and the environment. Every $1 invested in public transit yields $4 in economic benefits.”

Now, realistically, this is the definition of a long-term project. The extension of Metro to Dulles Airport and Loudoun County took decades. But the growth at Fort Belvoir has really changed things in southern Fairfax County, and it’s only going to get bigger there.

Del. Scott Surovell, whose district covers much of the Route 1 corridor in Fairfax, noted that the Ft. Belvoir garrison commander recently told a local town hall meeting that 62,000 vehicles travel to and from the base, with minimal mass transit, compared with 31,000 at the Pentagon. The new base hospital, which replaced the Walter Reed Army Hospital in the District, brings more traffic and the new National Museum of the U.S. Army is projected to bring 750,000 visitors annually when it opens in 2017.

Surovell also said traffic coming into Fairfax from Prince William in the morning is heavy, and heavy again heading south at night.

In the western Fairfax and eastern Prince William areas near a possible Orange Line extension, the legislation estimates population growth of 681,000 people by 2025. An increase of 100,000 people is forecast by 2020 in the areas of the Blue and Yellow Line extensions in southern Fairfax and northern Prince William.

Then there’s the job growth projected to occur in Prince William. In a recent Metropolitan Washington Council of Governments study, Prince William’s job growth is projected to be 108 percent by 2040, the greatest jump in the D.C. region. The top five job growth areas were all in Northern Virginia.

Connolly, whose district includes Prince William, has been talking Metro to Prince William since 2011. “The job growth is going to be here,” he said the other day. “And yet the infrastructure is not there to meet it. This bill is an important step in that direction."

I called Metro for their thoughts and did not hear back from them Monday. But as we know, it’s a long-term project.