Work continues on the Washington Metropolitan Area Transit Authority Silver Line project in Tysons Corner, Va. (Nikki Kahn/THE WASHINGTON POST)

Remember this the next time the D.C. region proposes to expand Metrorail: The Red Line is the only one of the five lines not connected with another. Anytime we push more people into the transit pipeline, it affects the riders already inside the pipe.

The region began to grapple with the reality of this formula last summer, when Metro realigned rush-hour train service. The second shock to the system will occur near the end of 2013, when trains on the new Silver Line begin to merge with those on the Orange Line, which bumps trains from the Blue Line and pushes some over to the Yellow Line, which shares a tunnel with the Green Line.

From east to west along the new route, rail and bus riders will be asked to make adjustments, some breaking commuting habits established over many years. These are the main elements of the service plan:

East side

This is a relatively small change for riders, though the reasons behind it are interesting. Since summer, when Metro began the program known as Rush Plus, eastbound Orange Line trains have traveled to New Carrollton, their historic destination, or to Largo Town Center, the usual destination for Blue Line trains.

When the Silver Line opens, Blue Line riders on the east side no longer will see Orange Line trains. Instead, the Silver Line trains will continue to Largo.

This was not the original idea. Eastbound Silver Line trains were supposed to unload their last passengers at Stadium-Armory, then move to a pocket track a mile and a quarter away on an aerial structure above the east side of the Anacostia River, and reverse direction.

But with the opening of the new line in sight, Metro managers took a fresh look at that turn-back. “It just kept raising more and more questions,” Dave Kubicek, the transit authority’s deputy general manager of operations, told Metro board members this month.

A train moving toward the pocket track would have to slow considerably and make a precise maneuver in a short distance to make the system work. It could have backed up rush-hour riders on the Blue, Silver and Orange lines going through downtown Washington.

Under the new plan, the line to Largo will have as many rush-hour trains as today. Metro will have to take that hashed orange line off its map and replace it with a solid silver line.

The middle

Figuring out the service pattern in the tunnel from Rosslyn through downtown Washington to Stadium-Armory involves the most complicated math for the Silver Line addition.

Metro can put a maximum of 26 trains per hour through the tunnel at Rosslyn. Today, the Blue and Orange lines account for those 26 trains. When the Silver Line opens, its tracks will join with the Orange Line outside East Falls Church. The Silver Line will send additional trains toward the Rosslyn tunnel at a rate of one every six minutes.

What gets subtracted?

Turns out Rush Plus was just Phase 1 of the Blue Line cutback. When Rush Plus started, the line went from 10 trains per hour during the rush to seven. Once the Silver Line is added, Blue Line service will be reduced to five trains per hour. That’s one train every 12 minutes. (Metro officials said some of those trains will be eight cars long, rather than the six cars that is standard on the Blue Line.)

One of the Blue Line trains will shift to the Yellow Line, which serves the middle of downtown. The riders who lose the most under this setup are those whose destinations are on the far west side of Washington, or Rosslyn, or the other stations in Virginia served by the Orange Line.

These are the commuters who have no better rail option than to board Blue Line trains that are likely to be more crowded.

Metro Board member Mary Hynes, who represents Arlington County, noted the continuing interest of Virginia jurisdictions in enhanced bus service between Pentagon City and Rosslyn. “We really can’t have this be a second thought,” she said. “Funding this bus service to fill in this gap . . . is a regional problem.”

West side

But the Blue Line riders aren’t the only ones who will be asked to adjust. Orange Line riders also will be affected in several ways.

Before last summer, 16 trains per hour operated on the Orange Line during peak periods. Under Rush Plus, that increased to 19. Once the Silver Line is added, the number of peak-period Orange Line trains will drop to 11. Inbound from East Falls Church, the reduction should not be an issue, because those tracks also will carry 10 Silver Line trains per hour at peak. But for the stations to the west, out to Vienna, it’s a cutback.

Metro officials expect many commuters will switch to the Silver Line, theorizing that they will find it more convenient to park at the Wiehle Avenue station in Reston. That’s the only one of the five new stations designed to have adjacent commuter parking. The other stations are clustered farther east in Tysons, where planners hope to reduce the dominant role of the car in commuting.

Some commuters will be deliberately redirected to the new stations, because their bus routes will shift to them after the Silver Line opens. Schedules are not final, but according to plans, all new stations will have bus service.

The Fairfax Connector will provide most of the local bus service, including new circulator routes with stops at the four Tysons stations. The transit authority will reroute some Metrobus routes to stop at the Tysons stations. Metro officials anticipate that Loudoun County buses will stop at the Wiehle Avenue station. Prince William County will direct bus service to Tysons, rather than to West Falls Church. The Washington Flyer service to Dulles International Airport will link with Wiehle Avenue.

“It’s going to be a very complex undertaking,” Kubicek said.