Dear Dr. Gridlock:

I enjoy your column very much. I have been retired now for seven years, but how well I remember my efforts to commute from Southern Maryland to the District. I have a very economical solution to the access/egress problem on Metro trains.

Each train has two doors, right? Why doesn't Metro advertise profusely for several weeks and then implement the following: Mark the doors boldly in large lettering, inside and out, with "Front Door - Enter Only" and "Back Door - Exit Only," and post large signs inside the cars reading "Exit Through Rear Door Only."

Thus, everyone will know they can enter only through the front door. Upon arriving at their destination, passengers can exit through the rear door, leaving the front entrance of the car open for boarding passengers.

Is that idea too simple or radical for today's commuters?

Jacqueline D. Marini

Helen, St. Mary's County

Controlling the flow of passengers works elsewhere. Of course, each side of a Metrorail car has three sets of doors: one at each end and one in the center.

On the BART subway system in the San Francisco Bay area, customers line up on marked areas on the platform and board the cars politely in single file, I'm told, in contrast with the mad rush here to get on and off.

For a long time, Metro officials told Dr. Gridlock that marked entry points couldn't be used here because the Metro trains didn't have precise enough braking systems to halt at a specific, marked place on the platform; hence, lining up wouldn't work.

Now, however, Metro has made braking adjustments and plans to test platform markers at three stations: Union Station, Metro Center and Gallery Place-Chinatown. Test results could be ready by spring. A new, more urgent "Doors Closing" announcement also will be tested.

This is an important concept. I'm hoping it works here.

Dear Dr. Gridlock:

So the latest idea from Metro is to remove seats so people will fill the gap in the middle of the train [Dr. Gridlock, Nov. 17]? Won't happen.

Anyone who has ridden the New York subway, the PATH trains between New Jersey and New York City or the Chicago subway at rush hour knows that regardless of the seating configuration, people stand by the doors. In fact, some people stand by the doors even when there are empty seats -- and even if they are traveling long distances.

New riders have to fight their way through the standees to get to empty seats in the middle of the train, much less to get to standing room in the middle of the train.

Metro does need to plan for more riders. It can do that immediately by (1) adding more cars, so every train is eight cars long, and (2) reducing the times between trains during peak periods to three minutes (which is what the PATH system does).

On a long-term basis, Metro needs to figure out how to double track the system -- how to do that, I don't know, because the system was poorly planned with only a single track in each direction -- and to provide more parking spaces.

Finally, no one in Metro's management or its board of directors should be permitted to drive to work. It's easy to dream about making people stand when you're riding in your car. It's another thing entirely to dream about standing when you're the one doing the standing.

Joel Whitaker

Silver Spring

Here is the timetable for expanding Metrorail to eight-car trains:

* By the end of 2006, 20 percent of all trains will have eight cars.

* By the end of 2007, 30 percent of all trains will have eight cars.

* By the end of 2008, 50 percent of all trains will have eight cars.

The question of which lines get the eight-car trains has yet to be determined.

That is all that is in the pipeline now. Eight cars is the longest train a Metrorail station can accommodate.

It would be nice to have an extra track to allow for express trains, as in New York, but the cost of installing a new track now would be prohibitive.

Transportation researcher Diane Mattingly contributed to this column.

Dr. Gridlock appears Thursday in The Extra and Sunday in the Metro section. You can write to Dr. Gridlock at 1150 15th St. NW, Washington, D.C. 20071. He prefers e-mails, at drgridlock@washpost.com, or faxes, at 703-352-3908. Include your full name, town, county and day and evening telephone numbers. Dr. Gridlock cannot take phone calls.