Dear Dr. Gridlock:

You receive enough complaining letters. It's time to pat someone on the back.

My car pool companion and I have been daily riders of the Dulles Toll Road for two years. We are delighted with the progress and management of the construction of the two new lanes. Those responsible for the placement and removal of barriers have done a magnificent job of installing them when needed and then removing them immediately when no longer required.

Admittedly, we are westbound in the morning and eastbound at night but, as residence to workplace patterns change, that no longer qualifies as going against traffic. I can honestly say that we have never been held up because of construction.

Isn't it a shame that those lanes will be reserved for HOV {high-occupancy vehicle} riders. We all pay a hefty toll -- we should be able to use them. JOYCE W. CRANDALL McLean

Dr. Gridlock looks for these kinds of letters this time of year. It's hard to find them. Thanks for sharing.

The toll road, incidentally, is scheduled to be widened from four lanes to six lanes by next fall. State officials are thinking about an experiment with HOV-2 (instead of HOV-3) on Interstate 66, and if that is tried and implemented, the new restrictions on the Dulles Toll Road could be HOV-2 for the new, third lane in each direction. Stay tuned. Mall Exit Morass

Dear Dr. Gridlock:

My husband was having a slow day selling Christmas trees at our church on a Saturday, so he passed the time counting cars making illegal U-turns from Old Keene Mill Road at Spring Street in Springfield.

Between 2 and 3 p.m., 177 vehicles made turns from westbound Old Keene Mill. Of these, 53 made the legal left turn onto Spring Street; 46 made illegal U-turns, heading east on Old Keene Mill Road; 133 made U-turns through our church parking lot; and 65 made U-turns at nearby Garfield Elementary School.

During his observations, there were four near accidents at the school and two near collisions because of illegal U-turns on Old Keene Mill Road.

Cars make U-turns in the school parking lot during weekdays and are dangerous to the children. We have seen accidents at this intersection. Police give out tickets constantly. One time, my husband stopped every car turning around in the church parking lot, and 100 percent said they were headed for Springfield Mall.

Why can't we change the exit signs on Interstate 95 to say "For Springfield Mall, use Franconia exit?" EDNA RIZER Springfield

This problem was cited in the very first Dr. Gridlock column, more than four years ago. Several hundred thousand people visit Springfield Mall each week. Many of them are first-time customers and assume that they should take the I-95 Springfield exit to get to Springfield Mall. Actually, it's the next ramp south, the Franconia exit, that they should take. So people make illegal U-turns at the first opportunity, Spring Street.

Why couldn't the state put up a sign? It could, if it wanted to. The state official who originally responded to this complaint said the state won't put up a sign for a private commercial venture, and chuckled that maybe the mall should be renamed Franconia Mall to solve the problem. The state puts up signs for for such obscure entities as the Weems-Botts Museum, in Prince William County along I-95; you would think it could do it for malls, because they have become, in cases like this, the new downtowns of a community.

The Virginia Department of Transportation's new chief engineer for Northern Virginia, Claude D. Garver Jr., recently told the doctor he would consider such a sign.

If you're wondering why the state allows those blue signs advertising fast food restaurants, gas and lodging, it's because that is an institutionalized courtesy on Virginia's interstates, to let motorists know what is coming up at off ramps, rather than notice of one-time commercial entities, such as malls (I know that is hardly a satisfactory distinction). If you're wondering why there is a sign on I-95 announcing Potomac Mills in Prince William County, the state maintains that is because Potomac Mills is an area on maps, like Dale City or Woodbridge, and that is what is being announced, not a mall.

Please, just put up the mall signs. Thank you. Remembering Your D.C. Registration Dear Dr. Gridlock:

Attention Vehicle Owners: The latest D.C. scam for raising funds is upon us. You may think that about a month before your current vehicle registration expires that you'll receive your normal reminder by mail. Well, it cost my daughter $100 and a wasted day at the Bureau of Motor Vehicles and in traffic court to learn otherwise when she was ticketed for an expired registration.

At the Bureau of Motor Vehicles, the answer to her inquiry as to why she had not received a mail renewal application was: "Oh, well, we've been having some problems there lately." Later, at traffic court, the adjudicator told her, "Sorry, but mail notices are only a courtesy, and it's your problem to be properly registered." No mercy. $100.

Mayor-Elect Dixon please note: If you are wondering why D.C. residents are so cynical about how they are served by the D.C. government, it's because of situations such as these. As taxpayers and constituents, are we not entitled to be treated with more consideration than this? At least a public notice alerting us of a change of policy would show concern for its citizens. ANDREW M. WERTH Washington

Your outrage is understandable, Mr. Werth. We've all become so dependent upon those renewal notices that internal alarms don't automatically go off if we never get a renewal notice.

There is no change of policy, though. The city tries to get the notices out about a month ahead of expiration. But with 20,000 renewal notices a month, some are invariably not going to be delivered. Best bet is to be aware of the expiration date of your license tags, and if you haven't heard from the city within, say, three weeks of expiration, call 202-727-6680 and ask to be mailed a form. The city prefers responses by mail.

You also can pay in person by going to the bureau's offices at 301 C St. NW between 8:15 a.m. and 3 p.m., or at 616 H St. NE between 11 a.m. and 7 p.m. Racing Down to Florida and Back Dear Dr. Gridlock:

Having recently returned from my annual round-trip drive to Orlando, Fla., I am pleased to notice that Virginia, the Carolinas, Georgia and Florida have finally raised their speed limits to 80 mph (65 posted), for most of the way.

Trucks, of course, are still exempt from all laws governing speed, or any requirements for common courtesy, but by staying out of their lanes, it is still possible to drive a four-wheeler 2,000 miles in relative safety and in a reasonable period of time. The use of cruise control set at 15 mph over the posted limit won't allow you to pass anyone, but you'll be moving with the traffic and the truckers will allow you to remain on the pavement. E.L. COWLEY Springfield

There's something to be said about keeping up with the traffic flow, Mr. Cowley, but 80 mph? You were lucky you didn't get nailed by police, or worse.

In Virginia, anything 80 mph and above is considered reckless driving, not simply speeding. The state is worried about the reduced reaction time and the greater probability of damage and injury at that speed.

Although you may have evaded radar on the round trip this time, you're still at risk. And a risk. Please slow down. Stuck in Metro Center With a $20 Bill Dear Dr. Gridlock:

It is evident from your Dec. 14 column that either you don't ride Metrorail or you've not been in the Metro Center station. For reasons unfathomable to me, there are NO Farecard machines that accept $10 or $20 bills at Metro Center.

If Metro's explanation for not having the machines at National Airport is because there are "only" 5,000 patrons, I would be interested in hearing the reason why there aren't any big bill machines at this very busy hub. AUDREY GOWEN Silver Spring

You're right about Metro Center being much busier, about 25,000 boardings a day. Metro's explanation on the lack of big bill machines is that there are only so many of these machines to go around the system, and Metro Center can get by without them better than some others because there is a sales center at Metro Center. It is located near the 12th Street exit on the Red Line level, and will take large bills.

Metro, as noted before, is in the process of replacing all its Farecard machines with ones that will take tens and twenties. This phase-in will cost $10 million and take place over the next few years. National Airport and Metro Center are scheduled to get the new machines next spring. An Ear-Popping Train Ride Dear Dr. Gridlock:

As a devoted and loyal Metro rider, I am puzzled by a recurring phenomenon: Why do my ears snap, crackle and pop at certain points on the Metrorail system? This painful experience seems to occur most often when a train in which I am riding accelerates rapidly. It is always accompanied by the bending and snapping of the car windows.

Aided by some co-workers, I have come up with two possible explanations:

1. A change in air pressure caused by an increase or decrease in elevation, not unlike that which occurs when an airplane takes off or lands, or an elevator rapidly ascends or descends.

2. An increase in air pressure that occurs because the train is moving at a faster rate than the air it is displacing can be expelled from the tunnel.

Is either explanation correct, or is there yet some other reason for my discomfort, as well as that of other riders? LENORE BARKAN Rockville

Both of your points apply to the ear popping. The Metro cars are not pressurized, so rapid changes in elevation or movement into and out of confined places can cause ear problems. Because of many complaints, Metro some time ago reduced the speed limit at its fastest points: from 65 mph to 55 mph between Foggy Bottom and Rosslyn, and from 75 mph to 50 to 55 mph on the long, straight stretch between Bethesda and Medical Center. Now Metro trains are not supposed to exceed 55 mph.

If you notice repeated ear problems at specific points, please write back. The Great Metric Debate Dear Dr. Gridlock:

If we're all supposed to be "going metric," why don't we have any speed limit signs in kilometers per hour?

I realize there's a big disadvantage to the communities that go first and suffer all of the confusion, but as the nation's capital, shouldn't we be leading the way? CATHERINE C. KELLEHER Rockville

This one makes my radiator boil over. PLEASE, PLEASE, not metrics. Isn't it enough we have to deal with gridlock without having to learn a radically different system of measurement? Do we know what it means if an exit is 30 kilometers ahead? Do we want to know? How big is something five centimeters long? What amount is 10 liters of gas? How many miles does your car get to the liter? How many liters does it hold?

If conversion to metrics is slow in coming, maybe it is because the public DOES NOT WANT TO LEARN A WHOLE NEW MEASURING SYSTEM. Why should we? If the case has been made, I've missed it. Is it to be on the same measuring standards as other countries? Not worth it. How many of us regularly travel abroad to the extent our whole nation has to relearn its measuring standards?

Are we ready for metrics? Do we want metrics? Whose idea was it to impose metrics on us? Was there ever any kind of vote on this? My guess is the answers are no, no, don't know, and no.

This should bring out the fans of metrics. If so, let's talk. Maybe there are many crucial issues the doctor is missing. As you readers so often say to Dr. Gridlock, thanks for letting me sound off. Fix Those Broken Headlights Dear Dr. Gridlock:

I do a lot of night driving. Lately, I notice many cars with only one headlight. I've had some harrowing experiences lately on unlit, two-lane roads. It's almost impossible to judge the width of an oncoming vehicle under such conditions.

It's a good thing Virginia has yearly safety inspections. I hate to think how bad the situation would be without them. SEYMOUR M. FROMM Alexandria

A guess would be that people neglect to fix this problem because they are not aware of it, or because the busted light may be only one of many car problems that need fixing, and therefore dropping off the car should be put off as long as possible for expense reasons.

What folks might not realize is that some of the express oil change facilities, or local garages, will quickly change a bulb for a small labor charge, plus the cost of the light. A New Year's Resolution Dear Dr. Gridlock:

A New Year's Resolution: Replace all "Slower Traffic Keep Right" signs with "Keep Right Except To Pass."

Make this a law.

Enforce it.

I believe at least 50 percent of gridlock will be eliminated. ROBERT J. KIRCHNER Derwood

Please feel welcome to pass along your New Year's resolutions for area officials.

Dr. Gridlock appears in Metro 2 each Friday. 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.