Dear Dr. Gridlock:

Why is there is no discussion about the overcrowding that is bound to result after Silver Line trains finally join Orange and Blue on the track through downtown?

It is impossible to run trains more frequently in rush hours, so the frequency of Orange and Blue trains will be decreased to make space for Silver ones, and rush-hour crowding will increase further.

Lengthening all trains to eight cars will not solve the problem. Can we face up to the need either to add a third or even a fourth track to the existing line, or build an entirely new line across downtown?

I have the impression that Metro is not willing to do more than mention the question, since it is a question of spending billions. (Cars, planes, and trains all cost billions.)

— Peter Bridges, Arlington

The transit authority leaders are very willing to raise the issue of expanding train service in the center of the D.C. region, which indeed will cost billions of dollars and demand large financial commitments from local jurisdictions.

The transit staff envisions a phased program that would gradually allow more people to use the system and perhaps provide a more comfortable ride for those already using it.

First and foremost, Metro wants to make all the rush-hour trains eight cars long, instead of six. But that’s as long as trains can get without rebuilding platforms.

Then there’s a plan to work around the bottleneck where the tracks come together at Rosslyn to go through downtown. Most ambitious is the idea of creating another tunnel with more stations through the middle of the District.

But most of us — especially Metro riders — don’t live in Tomorrowland.

Today, many riders on the Orange and Blue lines fear that Metro is aiming a Silver bullet at them, and they’re wondering if they can avoid getting hit.

Looks like it will depend on where they stand. At many stations in the middle of the rail system, rush-hour riders will have the same level of service they have now. If you wait at a platform anywhere between East Falls Church and Stadium-Armory, Metro won’t be subtracting trains. There will just be a new color to look for.

Bridges lives a bit under two miles from the East Falls Church station. He should do all right when the Silver Line opens, an event Metro officials now hope will happen this summer. If he waits on the platform at rush hour for a train to Capitol South, where he travels so he can do research at the Library of Congress, he can take his pick of Orange or Silver line trains. Twenty-one inbound trains should arrive at East Falls Church per hour during the morning rush, 10 on the Silver Line and 11 on the Orange Line, according to Metro’s plan.

Bridges and other riders who board between East Falls Church and Court House should find rush-hour service slightly more frequent than today. Off-peak service will become more frequent from East Falls Church all the way through to Largo Town Center at the east end of the line.

So everybody wins? No. If you’re waiting on a platform between Vienna and West Falls Church, the far-west part of the Orange Line, you lose once the Silver Line starts. You go from 17 trains per hour during the morning rush to 11.

If commuters stick to their travel patterns, then those Orange Line trains are going to be a lot more crowded. Metro hopes that many of you will move over to the new Silver Line stations, and Metrobus and Fairfax Connector routes are being adjusted toward that goal.

But there’s certainly no guarantee that commuters will eagerly follow Metro’s suggestion on that. Blue Line riders already have taken a hit in the Silver Line planning. During this long run-up to opening the new line, they lost trains.

Metro officials urged them to take Yellow Line trains to and from the Virginia stations. Many balked at this behavior-modification effort, either because they didn’t want to transfer trains downtown or because the transfer Metro had in mind just didn’t work for their particular route.

For those Blue Line riders, things will worsen when the new line opens. Blue Line trains will be 12 minutes apart, whether at rush hour or off-peak times. That will be the biggest rush-hour gap between trains in the Metrorail system.

This really hurts if you work on the west side of downtown, or if you take the Blue Line to Rosslyn and transfer, because your job is in the portion of Arlington or Fairfax served by the Orange Line.

These are among the commuters who won’t be impressed by big plans for more train, more tracks and more tunnels.

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 .