The Greensboro Station along Metro's new Silver Line looking east along Leesburg Pike. (Jahi Chikwendiu/The Washington Post)

The recent history of Metrorail’s expansion offers some guidance on what to expect when the Silver Line opens this summer — up to a point.

The first extension beyond the original system occurred a decade ago. That was the three-mile addition along the Blue Line out to Largo Town Center. It went rather smoothly compared with the previous big opening on the Green Line in 2001, and that’s where we see more of the challenges facing Metro and its riders.

In January of that year, Metrorail opened five stations to complete the Green Line along the 61 / 2 miles to Branch Avenue. Just before the extended service started, The Post’s Lyndsey Layton wrote that Metro expected the additional stations to draw thousands of new riders from Prince George’s County and Southern Maryland:

“New trains ordered to serve those riders are not ready for service, but Metro officials say they have enough cars to handle the extra riders until the new trains start rolling in late winter.”

Turned out they were wrong. Ridership immediately exceeded Metro’s expectations.

A few days later, Layton wrote: “The opening of five Metro stations has poured nearly 20,000 new daily riders onto the Green Line, overwhelming platforms and packing trains.”

Metro quickly had to add rail cars to the line, drawing those extra cars from the rest of the rail system.

That sort of history will get the attention of today’s transit riders. At the time the Green Line stations opened, Metro was awaiting the arrival of new rail cars. On the eve of the Silver Line’s opening, Metro is awaiting the arrival of new rail cars. The transit authority says the current rail fleet can handle the initial demand.

Many Orange Line riders who board trains at stations from East Falls Church through Rosslyn have expressed concern that their platforms will become even more crowded when the Silver Line opens. (Eastbound Silver Line trains will start from the new station at Wiehle Avenue, join the Orange Line tracks before East Falls Church and continue to Largo Town Center.)

Yet there are important differences between the Green Line scenario and the Silver Line situation.

In 2001, Metro had many fewer rail cars. And on the Green Line, the transit authority was running four-car trains, easily overwhelmed when the initial ridership exceeded expectations. The Metro fleet now consists of six- and eight-car trains.

The new Green Line stations at Branch Avenue, Suitland, Naylor Road and Southern Avenue offered parking. Only one of the five new Silver Line stations — the one at Wiehle Avenue — has a parking garage.

In fact, the initial success of the Silver Line depends in large part on complicated plans to get thousands of Orange Line riders to switch to the Silver Line via new bus routes.

This effort involves a lengthy publicity campaign, but it’s difficult to tell how many commuters will behave as planners hope.

Metro’s most recent effort at behavior modification had mixed results. When the transit authority cut back on Blue Line service while adding rush-hour trains to the Yellow Line in the Rush Plus program, Metro urged Blue Line riders to consider the Yellow Line as an alternative.

“We learned in Rush Plus that commuter habits are very deeply held,” said Metro Assistant General Manager Lynn Bowersox, who oversees the Silver Line marketing campaign.

If commuter habits are an issue with the Silver Line opening, we should send most of our sympathies to the many thousands who now board between Vienna and West Falls Church. They will have fewer trains at rush hours and will face greater crowding if many of their fellow riders refuse to switch to the Silver Line.

Metro’s publicity campaign for the Silver Line is beyond what we saw before the Green Line stations’ opening. But even if it’s successful in making commuters aware of the basic changes in service, there are plenty of details only experience will teach.

For veteran commuters, the work trip proceeds autopilot. They know the garage level where they’re most likely to find the first available space; where the bus will let them off and how different the actual trip time will be from the scheduled time; where to stand on the train platform so they can exit close to the escalator at their destination stations.

When the Silver Line opens, Metro plans to have extra staff on the platforms — the old platforms along the route, as well as the new platforms — to answer questions.

The biggest lesson history offers isn’t that a past problem will repeat itself. It’s that something new will surprise us.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071, or e-mail .