Dear Dr. Gridlock:

Metro trains often come to a stop with a series of repeated jerks and jolts. Even if you believe the train has finally stopped and it's safe to walk toward the doors, another big jolt will throw you across the aisle.

You can tell the seasoned commuter from the tourist by when they decide to stand up and wait for the doors to open. The tourist will usually get flung a couple feet before desperately grabbing for a handrail.

When the cars are crowded, everyone has to hold on for dear life. This is not always possible, and I have been on both sides of many toe-troddings and unintentional shoves as well as complete spills.

Is there anything the drivers can do to prevent those jolts? It seems some days, drivers or trains are better than others. Is the problem mechanically irreversible? If so, passengers should be warned of the danger. STEPHANIE WISE Arlington

You've fingered a problem, Stephanie. Metro has been aware that some of it's trains lurch to a halt and now has pinpointed the problem to a defective microchip in the braking system of some cars. Metro is replacing those defective components and expects to finish this spring, according to spokeswoman Beverly Silverberg.

Most Metro train trips are controlled by computer, and the operators have no role in how the train stops. The brakes on all cars are electronically applied, but the microchip problems seem isolated to the newer model cars, which are identified by a number in the 2,000 or 3,000 series. The older model cars, those in the 1,000 series, do not seem to have those problems. Thanks for pointing that out, and until things get fixed, hold on!

The Metric Argument

A reader recently asked why we don't get on with the change to the metric system and convert all of our road signs to kilometers and meters. That suggestion did not sit well with the doctor, who responded with "an uncharacteristic outburst," as one reader later put it. With all the other commuting stress we encounter, it just doesn't seem to make sense to convert to an entirely new system of measurements. Does that help us in any way? Why should we do that, the doctor asked. That brought out a number of pointed letters, among them:

Dear Dr. Gridlock:

Shame on you and your archaic attitude toward the metric system. You typify the American problem of resistance to change.

Have you ever actually used the metric system? Ask any engineer or scientist: It's great and it's used almost everywhere else in the world. The beauty of metric is its simplicity. Who cares if there are 5,280 feet to a mile, or 2,640 feet (880 yards) to a half-mile? Half a kilometer (1,000 meters) is 500 meters; a quarter of a kilometer is 250 meters.

Who wants to remember that water freezes at 32 degrees Fahrenheit, or boils at 212 degrees Fahrenheit? Metric is easier: Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.

If you used metric for two or three years, you'd wonder why we didn't do it sooner. Let's get into the 20th century. STEPHEN MILLER Falls Church

We stopped the metric conversion process when the politicians heard the public scream, "WE DON'T WANT TO LEARN A WHOLE NEW MEASURING SYSTEM." Sounds a bit like a child not wanting to learn the multiplication tables.

Many of us travel and work throughout the world. Why not make things easy for ourselves and adopt the metric system? It would certainly be better for our economy. It also might demonstrate to the world that we aren't as self-centered as we appear.

It will take anyone a few hours to learn the metric system once one is immersed in an area that uses it. It may cause us to think a little, but soon the pain is over. If we try to adapt slowly to the system (as was attempted in the 1970s) we will never learn it, because we will always have the easy, old way to fall back on.

It really isn't that hard. If the wording on our traffic signs were changed today, we could be metric by tomorrow. WILLIAM G. REED Bethesda

Your response to the metric question should indeed bring out the metric fans. You asked, who cares? The answer is simple -- everyone who wants a job with a future!

Like it or not, we are part of a global economy. The Pacific Rim and the European Community, now augmented by Eastern Europe, are large, growing markets.

Our future economic health will depend critically on increasing our participation in those markets. These countries are ALL on the metric system. Our multinational corporations have, in fact, made this transition. Those who wish to be suppliers to those corporations or compete in the international market directly also will have to make this transition.

So the more we can do to help Americans become metric literate, the sooner we can become more competitive. ROBERT M. WHITE Under Secretary for Technology U.S. Department of Commerce

Well, here in the back of my cave, Dr. Gridlock sees your flashlight, Mr. Under Secretary. Eventually, as we have a true global economy, we may have to go metric. But that day has not come. Once it can be demonstrated in a very real way that we as individuals are adversely affected -- in the pocketbook -- by our current standard of measurements, then the popular support may be there to change. Right now it is not. Congress tried to impose metrics on a voluntary basis in the 1970s, and some gasoline stations switched to liters and various committees were set up. But the people didn't want to change. Gas stations went back to gallons. Let me close with a letter from a fellow true believer: Dear Dr. Gridlock:

I was surprised and pleased to hear your voice of reason in the metrification debate. Here are a few more arguments in favor of our current method of measuring distance.

First, the metric system was developed by the French. Rather than base the system on the human body, they decided to create a system de novo (Latin for "out of stupidity"). Thus, unless one happens to have a meter stick with them, it is difficult to judge any distance.

The English system, which we use, is, on the other hand, based upon body parts. Thus while a meter is about the length of your meter stick, a foot is about the length of your foot. An inch can be approximated by the width of your thumb, or, for those with smaller hands, the length of the middle digit of your forefinger.

A yard is about a step long or, when measuring rope, the distance from your nose to the end of your hand. A mile is about a thousand paces.

Other than the French, it would seem that the primary advocates of the metric system are scientists, who claim it is easier to work with. That should be tempered by the fact that they also claim that logarithms are easier than real numbers and that calculus makes sense.

Let me strongly second your plea to retain the system that we all know and can use without a conversion table. Let the rest of the world do what it wants; we've got it right. DAVID A. PATTON JR. Arlington

Dr. Gridlock appears in this section each Friday to explore commuting matters. He'll try to find out why bad situations exist and what is being done about them. You can suggest topics by writing (please don't phone) to DR. GRIDLOCK, The Washington Post, 1150 15th St. NW, Washington, D.C., 20071. Please include your full name, address and day and evening phone numbers.