Quick: In Northern Virginia, where is Exit 5 on the Capital Beltway? Give up? Well then, of course you know the proper name for Exit 19B from I-66. And what road from I-395 you are on if you take the famous Exit 3A.

You should know the answers, because when it comes time to get off these interstate highways, those will be the only signs you see.

Why is this so? The good folks who coordinate information on interstates in Northern Virginia provide signs that describe the actual names of the roads at exits, but those signs are somewhere in the mile before you get to the exit. If your mind has wandered, and you can't quite recall whether the next exit is the one you want, often all you get at the point of departure is a sign like the one that says: "Exit 19B." Good luck.

Who knows exits only by numbers? On freeways in other states, California for instance, there are signs for miles in advance advising what streets are coming up and how far away they are. Then, directly over the exit ramp, is a large sign that names the street at that particular exit. These signs are big enough to be seen from a great distance, and allow motorists plenty of time to decide what to do as they approach an exit.

Virginia, for some reason, does not do things this way, at least in Northern Virginia. Instead, you get only Exit 19B at the moment of decision. How many people have missed their exit because they couldn't remember if that was the right one? Or how many have taken the wrong exit for the same reason. Asked why there shouldn't be names at exits, Virginia highway department spokeswoman Marianne V. Pastor said: "That's a fair question. We'll look into it." The District and Maryland seem better at providing more precise signing at points of exit. While we're on interstate signs, the Virginia highway department should get lots of credit for pioneering signs on interstates showing the way to gas, food and lodging. But this is also the department that declines to put up signs on interstates to nearby major Northern Virginia malls such as Springfield Mall and Fair Oaks. These malls have become the suburban Main Streets of their areas and draw hundreds of thousands of people a week, many for the first time. The department has no trouble providing prominent signs along I-95 for such facilities as the Weems-Botts Museum at Exit 51 in Prince William County, and, a little farther south on I-95, the G. Melchers Memorial Gallery. Pastor promised to look further into signing for malls, too.

P.S. For those taking the quiz: Exit 5 off the Beltway is to Braddock Road; Exit 3A off I-395 connects to eastbound Duke Street, and Exit 19B off I-66 is to Leesburg Pike and Tysons Corner.

Meanwhile, here's another question. Can Metrobus drivers call police to solve traffic jams? Read on.Dear Dr. Gridlock:

There was a long backup this morning on Georgia Avenue southbound, starting at Colesville Road. Apparently the lights one block west on Colesville were messing up traffic, and everyone was causing gridlock at Georgia Avenue and Colesville Road. The bus I was riding on took 20 minutes to travel one block. Most of the passengers gave up and got off to walk the rest of the way to the Silver Spring Metro. No one was getting through the intersection in the two right lanes, no matter how many light cycles we sat through.

After I got off I noticed a county police officer on a motorcycle sitting on the corner where the lights were out of sync. I told him about the gridlock situation, and he went up to the intersection involved and within seconds traffic was flowing smoothly on Georgia Avenue.

Doesn't the driver of a Metrobus have the ability to notify the police, at least indirectly, of a situation such as this? The jam-up on Georgia Avenue must have been two or three miles, and still the police hadn't noticed or done anything about it on their own. Was it just a lack of initiative on the part of the several Metrobus drivers stuck in traffic or is it something that is not possible? STEVE MILLER Silver Spring

Metrobuses are equipped with radio communication only with Metro's central office. Drivers generally use this communication to get help for a disabled bus, for emergency medical attention or to summon police to the bus. According to Metro spokeswoman Mary Bucklew, "We encourage bus drivers to call Metro central and report traffic jams. The bus drivers do so frequently and Metro central then notifies the proper authorities."

Let's hope this letter helps encourage Metrobus drivers to report more traffic jams, and we'll continue to hope that more police will get off their motorcycles and out of their cruisers to deal with traffic jams around them. Such problems may not be as challenging to police officers as solving a major crime, but resolving traffic jams means a great deal to an awful lot of people. Despicable Spitter Dear Dr. Gridlock:

One evening during the rush hour, I was traveling north on 18th Street NW. A fellow parishioner was riding in the car with me as I drove. As I was proceeding, a "messenger biker" rode his bike into the path of my automobile. I was driving in the second lane from the left curb, proceeding north on this one-way street. The biker rode his bike in and out of the lane, slowing down, starting up, weaving back and forth. Because it was unclear what this biker planned to do, I drove behind him for a while and then lightly tapped the car horn to alert him to my presence. (I also ride a bike and have a sense of how a horn can startle a biker, which is why I only tapped the horn.) I saw no other alternative in the circumstance.

The biker slowed down, came near the side of the car and screamed an obscenity. He then rode his bike to the front of my car and using his fist, pounded on the front end of the car. At the next stoplight, he came to the side of the car and, through my open window, spat in my face. When I had registered what had actually happened, he had long gone, weaving his way through rush-hour traffic. The parishioner who rode in the car with me shared the same shock with me.

Two things I learned out of this experience: Not all of the messenger people are completely ego-intact; and the practical application of Jesus' instruction to pray for one's enemies is often most sorely tested in Washington traffic.

Something must be done to regulate the messenger bike people. Too many of them flaunt traffic rules and endanger others. I would suggest a regulation requiring bikers to have shirts with license numbers on them along with license tags on the bikes. Additionally, the name of the messenger service should be imprinted and visible. THE REV. KENNETH A. BASTIN Washington

This subject has been covered here before. Police say that bicyclists are subject to the same rules of the road as automobiles. Yet we've all seen bicyclists who ignore all rules, including red lights, and zip recklessly around city streets in a way that endangers drivers, pedestrians and other bicyclists. At the same time, bicylists respond to this complaint by pointing out how law-abiding most of them are and the awful things motorists do to them. What is needed here is for police to enforce traffic laws against bicyclists who break the law, as well as motorists who break the law. That should lead to safer streets.

Don't Do Windows

Those popular yellow signs in car windows announcing "Baby on Board" soon will be illegal in Virginia unless the car is equipped with mirrors on both sides.

Beginning July 1, it will be illegal to operate a motor vehicle in Virginia with signs, posters or sunshading material on any window, with certain exceptions. Drivers will face a $15 fine plus court costs if they affix any signs that extend upward more than five inches from the bottom of the window or exceed 20 square inches in size, according to Capt. R.L. Bumgardner of the Virginia State Police. Cars with two side mirrors are exempt from the new law.

Bumgardner said the law covers all vehicles registered in Virginia and any vehicles driven through the state. College and high school decals are exempt if they fall within the size requirements.

The new law is needed because signs and posters in car windows, as well as much of the sunshading material now in use, restrict visibility and increase the potential for a traffic crash, according to state police.

Dr. Gridlock appears in this section each Friday to explore what makes it difficult to get around on roads, from misleading signs to parking problems to chronic bottlenecks. We'll try to find out why bad situations exist and what is being done about them. You can suggest problems by writing to GRIDLOCK, c/o The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Please include your full name, address and day and evening phone numbers.