Dear Dr. Gridlock:

I frequently come home via 16th Street after midnight. There is little traffic at this hour. Why can't the lights on 16th be set to blink yellow, like those in Montgomery County? THOMAS PHELPS Silver Spring

You would think this would be an easy and sensible thing to do. But, of course, it isn't. The city used to do this at some intersections, but found it was a headache. Some angry D.C. residents complained that commuters were speeding through their neighborhoods because of the flashing lights, and that the city was favoring the interests of commuters over the interests of its own residents. That sentiment seemed to come up at budget hearings, according to the city's traffic chief, George Schoene. Plus, the flashing yellow was just one more cycle that could malfunction in an antiquated traffic light system that had to be replaced. So the city stopped using flashing lights in 1987.

Now the the city has a new computerized traffic light system, but programming for flashing lights would take a study of individual intersections for need. With all the other demands on his people, this area is receiving a low priority, Schoene said. "I'd rather work on improving rush-hour timing rather than night timing that would affect a very few people," he said.

Montgomery County has no such difficulty. With the flick of a switch, the county turns many signals to flashing yellow, including some on its portion of 16th Street, between 12:30 a.m. and 5:30 a.m. It is all handled by computers. "It's really no problem," said Scott Wainwright, assistant chief of the county's division of traffic engineering. The intersections affected are those with little cross traffic. If there is poor visibility from the side street, or if residents complain, the county will visit the scene and make a decision case by case. Too bad the city can't do it. Toddlers on Metro

When children ride the Metro system at no charge, does that still entitle them to a seat? I see many infants and toddlers occupying seats during rush hour and have often wondered about the Metro policy on this matter. LYNNE ROCK Rockville

Metro doesn't have a policy on this. There are some priority seats, marked as such, near the doors for senior citizens, the handicapped and the pregnant. Otherwise, it's first-come, first-served. Metro would like to have infants and small children seated because it is safer for them. "It's a question of courtesy," said Metro spokeswoman Beverly Silverberg. "Wouldn't it be wonderful if we all were raised to be considerate of the elderly and those disabled and those clearly in need?"

Unfortunately, courtesy is not always evident. Read on: Dear Dr. Gridlock:

I am a frequent user of Metro's Red Line from Shady Grove to downtown. My blood pressure rises when I have made this commute between 3 and 4 p.m. on weekdays during the school year. Scores of young people enter the cars at Tenleytown, seemingly without regard that there are others around.

Last Friday, for instance, I was in car 3199 when we stopped for passengers at Tenleytown at 3:10 p.m. In came the after-school bunch, shouting, jostling and running. Two students were drinking cola, one was drinking juice. One girl was eating Fritos and another a candy bar. A boy was eating from a box of popcorn. And a girl entered the car eating a hot dog from a street vendor. Within four or five stops the boy was throwing popcorn at his friends and the hot dog eater was running away, dripping mustard and relish on the way. By the time I got out at Metro Center, car 3199 looked like an unkempt alley.

I realize that children that age are loud and unruly. Running, pushing and shouting are typical behaviors among them. But a definite violation of Metro rules occurs when they break out the food. I have called Metro several times to complain. Each time I was told that they are understaffed and don't have enough security people to monitor every car. I agree, but when an incident is repeated on a daily basis at the same time and same place, I would like to see some response. W. FRANK Washington

"We know that there are some stations -- and Tenleytown is one -- where students play on escalators and are rather rowdy," said Metro spokeswoman Marilyn Dicus. "We do station officers in plainclothes and do periodically stop them. But transit police have a lot to do, and try to spread themselves throughout the system so they appear to be everywhere at once." Anyone got any ideas for Metro on this? Barriers on Klingle Road Dear Dr. Gridlock:

What has happened to Klingle Road between Rock Creek Parkway and Woodley Road NW? It is now blocked off by large concrete barriers. As a result, all the surrounding roads are very congested each morning. My commute is increased by 10 to 15 minutes each day.

Granted the road has always been in terrible shape. Will it be fixed soon? What can we expect for a timetable? LEONARD FREEMAN Silver Spring

Klingle Road is closed between Cathedral Avenue and Porter Street because a sewer line has collapsed under the road. This has damaged the road, guardrail and retaining wall. The District is doing design work and getting permits from the National Park Service, which owns the right-of-way, and should be finished with that in six months. Then a construction schedule can be set. This is not good news; you can probably factor Klingle Road out of your commute for at least a couple of years. Beware of Curb at Bus Stop Dear Dr. Gridlock:

On Aug. 5, I had a nasty fall as I went to get on a Montgomery County Ride-On bus in the U-shaped driveway in front of the Silver Spring Metro. My leg banged against the bus stop. There was internal and external bleeding, the leg was swollen for over a week, and a lump is only now going down. I thought I was stepping from the sidewalk to the curb, but didn't see that the curb was badly eroded.

Later, I noticed there are three big gashes in the curb where the 6, 7 and 10 Ride-On buses stop. I tried to report it. Metro actually sent someone to look at it, and agreed that it is dangerous but said it was Montgomery County's responsibility because only county buses stop at that place. I had already called the Montgomery County Department of Transportation. It referred me to the transit administration, which said it is Metro's property and their responsibility.

Next, I called the county attorney's office. I told the person who answered the phone what I needed to know. She transferred me to an attorney who complained that he shouldn't be expected to know everything, and hung up.

After that, I called the office of the county executive. All that happened was someone from the Highway Department called to say it isn't in their jurisdiction.

This is mindless bureaucracy. I hope you can pierce the bureaucratic veil. The gashes in the curb are growing; a man running for a bus fell in one today. NANCY WILLIAMS Silver Spring

Gashes in a curb aren't among our most pressing transportation problems, but anyone who has gone to such lengths to get an answer deserves one.

It's Metro's responsibility. Beverly Silverberg, Metro's spokeswoman, pierced the bureaucratic veil. She said the problem should be fixed in 90 days. One would like to hope that Metro employees who visited the site for you would have been as enlightened as Metro's spokeswoman; unfortunately, that's not always the case. Meanwhile, watch your step. Complaints on Postal Drivers

Reader Edith M. Munro of Alexandria, in railing against red-light runners, noted here Sept. 7 that she reports commercial and government vehicles that run red lights. She observed that the Postal Service didn't seem to care. Now, a word from the Postal Service: Dear Dr. Gridlock:

Contrary to Ms. Munro's conclusion, the U.S. Postal Service is vitally concerned about the safe driving practices of our employees and, indeed, most of our postal drivers are true professionals. This is reflected by the 13 percent decrease in postal- related vehicle accidents in the metropolitan area compared to last year.

It is extremely unfortunate that Ms. Munro's calls seemed to reach only an unrepresentative sampling of postal personel.

For the benefit of Ms. Munro as well as your other readers, concerns or comments about postal drivers in Washington, D.C., or Maryland can be directed to me at 301-499-7314. Concerns or comments about postal drivers in Virginia can be directed to my counterpart, Ken Crawford, at 703-207-7661.

The only information that we need is a date, time, location, vehicle number (if possible) and description of the unsafe driving practice. We will follow up to ensure that the manager, supervisor and employees are made aware of the observation. GARY A. EMICH Manager Safety and Health Services U.S. Postal Service Capitol Heights

Thanks for the response. If only every manager were so concerned. Now, if somebody would just get that Coca-Cola truck moved from the 17th Street NW side of the Old Executive Office Building, where said truck double parks in the morning, narrowing 17th Street to one lane.

Dr. Gridlock appears in Metro 2 each Friday. You may write (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.