Over 24 hours, the American Legion Bridge handles the greatest volume of travelers, but at rush hours, Metro’s Rosslyn tunnel moves more commuters. (Chip Somodevilla/Getty Images)

Virginia’s highway engineers keep pushing their projects closer and closer to the American Legion Bridge, but they’re going to be out of options once their feet get wet. When they reach the Potomac River, they will need their counterparts in Maryland to extend a hand.

Virginia transportation officials would like to talk about the possibility of advancing the high-occupancy toll (HOT) lanes over the bridge and up the Maryland side of the Beltway to the Interstate 270 spur. And in September, Virginia’s Commonwealth Transportation Board probably will give them the okay to reach out for a chat.

If you are among the several hundred thousand people who commute on the west side of the Beltway, let’s pause here for a message: If there’s a way to telecommute, find it, or be stuck in that mind-numbing traffic for many years to come.

The states aren’t even talking yet, let alone looking to see whether HOT lanes actually can be made a part of the trans-Potomac Beltway.

Leaders on both sides of the river who think a new bridge farther west would make a lot of sense need to practice the art of the possible. Adding people-moving capacity at the Legion Bridge is at least possible, even if it’s still years away.

Top transportation officials in Richmond acknowledged as much this month.

“Maryland has publicly stated they’re not interested in any additional river crossings,” Virginia Transportation Secretary Aubrey Layne told members of the Commonwealth Transportation Board. “Okay, what’s the practical solution we can work on?”

His answer: Start talks about making life better for the people using the Legion Bridge.

Layne talks about the need to recognize the different visions of the two states. But he and his staff also make a good practical case for targeting the Legion Bridge, rather than focusing on a new one upstream.

The Virginia Department of Transportation has collected new sets of information on travel patterns at the Potomac crossings.

A relatively small portion of Legion Bridge traffic is carving out a big “U” commute. That sort of a trip might take a driver between a home in Frederick and a job near Dulles International Airport.

Many cross-Potomac travelers today — and very likely for decades to come — trace more of an “I” pattern, meaning the start and finish is close to the Beltway corridor. Another large group does an “L,” meaning that one end of the commute is close to the corridor while the other side splits off.

During the afternoon rush, the major origin points for the Beltway inner loop drivers are central Fairfax County (30 percent), western Fairfax (21 percent) and Arlington County/Alexandria (13 percent). The major destinations for this northbound traffic are eastern Montgomery County (44 percent), western Montgomery (19 percent) and the Baltimore area or other points northeast of the Washington region (17 percent).

Among those using the inner loop for their afternoon commutes, 14 percent are traveling from central Fairfax to eastern Montgomery, 10 percent from western Fairfax to eastern Montgomery and 6 percent from Arlington/Alexandria to eastern Montgomery.

Those heading from central Fairfax to western Montgomery, Frederick or points northwest account for 8 percent of the traffic. Five percent are heading from eastern Loudoun County and western Fairfax to western Montgomery, Frederick or points northwest.

In other words, a commuter is more likely to be going from Tysons Corner to Bethesda, Silver Spring or Rockville than from Herndon to Frederick.

It makes a better case for improving the capacity of the Legion Bridge than it does for building a bridge farther west, the one that would be of greatest benefit to the “U” commuters.

Another way across

The VDOT study compiled various forms of data to learn more about the 11 Potomac River crossings between the Nice Bridge to the south and the Point of Rocks Bridge to the northwest.

The Legion Bridge is the champ for total daily river crossings, with the 14th Street bridge and the Woodrow Wilson Bridge as runners-up.

But if you narrow that to commuter travel during peak periods, then look a bit downstream from the Legion Bridge for a bigger commuter-mover: Metro’s Rosslyn tunnel.

The study notes that the volumes at the Rosslyn tunnel exceed those on any of the cross-Potomac interstates at peak periods. Add the Yellow Line bridge trains to the Rosslyn tunnel trains, and you’ve accounted for about 35 percent of the morning peak crossings from Virginia.

As we’ve discussed in recent columns, the Rosslyn tunnel is under severe stress. It’s the biggest choke point in the Metrorail system, and Metro officials say it can’t handle the 26 trains per hour they’re trying to push through at peak periods.

They propose to cut back the number of trains for at least a few years, which will increase crowding on the Orange, Silver and Blue lines that merge at Rosslyn.

The problems that the next generation of commuters will have in crossing the Potomac can’t be solved by fixing one bridge or tunnel. But the Virginia study makes a good case for focusing on the problems at the Legion Bridge and the Rosslyn tunnel before devoting resources to a new western crossing.