Dear Dr. Gridlock:

While on business in San Diego, I was pleasantly startled to see that two people per vehicle qualified as a car pool. Not only does their approach show more common sense, but clearly indicates that San Diegans understand how hard it is to find more than two people living and working in the same part of town AND working identical hours.

I pondered this approach yesterday morning while another manager and I sat on U.S. Route 50 in Virginia, inhaling those fragrant fumes of rush-hour backup. Interstate 66 was the ideal route to paradise (and our meeting in D.C.) but there were only two of us in the car and (sigh) this isn't San Diego. I-66 inside the Beltway is for three-person (or more) vehicles.

One day, before we all succumb to backup burnout, I hope that local transportation gurus will come to the enlightened conclusion that while Carpool-2 isn't as nifty as Carpool-3, it surely reduces air/brain pollution better than Carpool-1. LYNNE JOHNSTON Falls Church

The short answer is that the interstate highways in Northern Virginia, where there are high- occupancy vehicle lanes, are too crowded to lower the requirements from HOV-3 to HOV-2. If they did, the express lanes would move too slowly to provide enough incentive for people to form pools and use them. At least that's the view of state officials.

The concept of setting aside lanes for the exclusive use of car pools has long been a focus of controversy. Some folks would like to do away with them, figuring any road paid for by taxpayers should be open to all. Virginia officials are strongly in favor of them, pointing out that by their count the Shirley Highway (I-395) carries 12,000 more people per rush hour in two HOV lanes than in the four regular lanes alongside. The car pool lanes also move faster.

Of the 40 HOV facilities nationwide, about half are HOV-2 and half are HOV-3 or more, according to a recent study by the Texas Transportation Institute.

The jurisdictions that opt for HOV-2 are usually in areas less densely populated than ours, according to Jim Hanks, who worked on the study.

The worry by Northern Virginia officials is that if the express lane restrictions were lowered to HOV-2, there would be so many more cars in the express lanes they wouldn't be express any more. About 25 percent of the traffic in regular lanes already has two people per vehicle, according to these officials.

Roads in Northern Virginia are already hopelessly congested. Most of those roads are rated level of service E or F, with F being the worst possible. An F grade means speeds on average of 20 miles per hour or less. Most of these roads are carrying two to three times the traffic that they were designed for. The Beltway, for instance, between I-395 and I-66 was designed for a capacity of 94,500 vehicles and carries 205,000 a day. I-66 inside the Beltway was designed for 47,300 vehicles and carries about 100,000.

One possible loophole here is that the state has no traffic count for capacity versus volume during rush hours on I-66. It is possible that the HOV-3 lanes carry light enough traffic to make that segment HOV-2.

"It's a legitimate question, one that might well be considered down the road," said Virginia transportation spokeswoman Mary Ann Reynolds. But she pointed out that these surveys are costly and time-consuming, and there are no plans to conduct any now. Instead, the state is focusing on opening an HOV-3 lane on a widened Dulles Toll Road next summer, and tying that into I-66, and in adding interim HOV-3 lanes to I-66 for eight miles between the Beltway and Route 50, due to open in 1992.

Metro Spider Alert

Dear Dr. Gridlock:

The Eisenhower Avenue Metro station is infested with spiders.

They are present in large numbers on the platform ceiling, clustering around the light fixtures. Besides the negative esthetics of the cobwebs, there is a very real danger that they could land on a passenger and bite. Many people are allergic to spider bites.

A regular cleaning and spraying of insecticide would alleviate this problem.

P.S. The spiders are most active and noticeable at night. SCOTT S. ELLIS Alexandria

Well, we all have our problems.

A Metro spokeswoman, Marilyn Dicus, promises that a maintenance crew will be out there within a week to get rid of the spiders. Would that every commuting problem were so easily solved.

Cyclists' Rules of the Road

Dear Dr. Gridlock:

I ride my bike everywhere. Here's what happened to me on my ride home today.

As I was riding up Burke Centre Parkway in Fairfax County, a blue sedan passed by and tried to run me off the road. The shoulder is gravel and is not for bikes.

I stayed on the road and let him know what was up with a not-so-friendly, yet ever-so-popular gesture. As he pulled up to the intersection, he stopped his car and opened his door. He asked me what my problem was, and I asked him what his problem was, and he said I should have been on the shoulder instead of the road.

I replied that bicyclists have the legal right to be on the road and that I had the right-of-way. He disagreed and, after a flurry of four-letter words, he asked me to pull over so he could kick my . . . .

I decided he wasn't worth my time, so I rode on to my house.

What's wrong with motorists in Washington today? I realize they work all day and are in a rush to get home, but why do this? A bicycle has just as much right to the road as motorists. Why can't they realize that? MATT WILLIAMS Fairfax

Probably because many of them don't know the rules. They vary according to jurisdiction. Here are the rules:

Virginia: Bicyclists can use the roadway, but should keep to the right as much as possible. Exceptions are interstate highways, and toll and limited access roads, where bicycles are banned.

On other major thoroughfares, such as U.S. Route 29 in western Fairfax, Prince William and Fauquier counties (posted speed limit 55 mph), bicyclists can use the right side of the right lane, but might be well advised to keep to the shoulder if possible. Obviously, common sense applies here too. As for Burke Centre Parkway, you were in the right, Mr. Williams.

District: Generally, there are no restrictions as to the use of the roadway by bicyclists. Normally, they are supposed to keep to the right lane, with slower moving vehicles, but that part of the law is vague and left to the discretion of the bicyclist, according to Tom Pendleton, the city's bicycle coordinator. There are no restrictions for use on freeways; common sense should apply.

"We had a report of one man who was occasionally commuting on the Whitehurst Freeway," Pendleton said. "We're hard put to say that M Street is any better for him. Obviously you wouldn't use the Southeast-Southwest Freeway because there are enough surface streets in good shape in that area."

Maryland: Bicyclists are allowed to use the roadway, but with these restrictions: no travel on freeways, expressways, interstate highways, and where signs prohibit bike travel on limited access roads (for instance, U.S. Route 301 on the Eastern Shore).

Beyond that, if the posted speed limit is 50 mph or more, bicyclists must use the shoulder of the road. If the speed limit is less, bicyclists can use the right lane, but must stay as far right as possible.

Sunday Shenanigans on the Yellow Line

Dear Dr. Gridlock:

This is about the peculiar schedule of Yellow Line Metro service on Sundays.

On many recent Sundays, Blue Line trains only have operated from the Huntington station. The Yellow Line trains shuttled between the Pentagon and Gallery Place, requiring a 20-minute wait amid much confusion at the Pentagon station.

On other Sundays, BOTH Yellow and Blue Line trains operated from Huntington. At some unknown time on Sunday afternoons, service returned to normal. This has been going on for months.

While there may be good reason for Metro to curtail service, I wonder why no attempt has been made to communicate with riders about this disruption. At such times, riders may double or even triple their riding times between Huntington and Gallery Place.

While unintelligible messages may be given over the Huntington P.A. system, they cannot be heard by passengers already seated on the trains. And if one boards an awaiting Blue Line train . . . will the next train be Yellow or Blue? The practice varies.

One cannot ask an abandoned kiosk any questions while the attendant is on break. How about some signs outside the turnstiles? DANA M. WEGNER Alexandria

Maybe we can do better than that. Here is the schedule, as provided by Metro on Wednesday: The only Blue Line train leaving Huntington Station departs at 9:52 a.m. Sunday mornings, to get in place to receive passengers further down the line. Because service doesn't officially open until 10 a.m., it's the attendant's call whether to allow early boarding.

From the 10 a.m. opening on, the only train you can catch is a Yellow Line one, according to Metro. They start leaving at 9:58 a.m. and then 10:13 a.m. and every 15 minutes thereafter.

This schedule does not square with your observations, but does give you Metro's latest (as last Wednesday) schedule. Please advise if this is out of whack with what you are now seeing.

How About Messages Drivers Can Use?

One reader inquires about the usefulness of the electronic overhead signs on Interstate 95 as it approaches the Capital Beltway in Prince George's County. Oftentimes the signs give such helpful tips as "Speed Limit Still 55/Save on Gas and Stay Alive," and the ever-popular "Room Inside? Share a Ride."

The reader asks why the signs can't be more helpful, providing detour routes into Washington when there are accidents on major entry routes.

These messages were a problem in Virginia, when similar ditties infuriated the public. Turned out those signs were not yet activated.

The Maryland signs do indeed work and do provide traffic emergency information, according to a state spokeswoman. They cost no more to carry the safety messages than to remain blank.

Sometimes Dr. Gridlock wonders about these electronic messages too. They advise congestion ahead, when it is gone by the time one arrives there, or seem not to report things one stumbles into. If anyone has any specifics, I'd like to check into it.

You can write to (please don't phone) DR. GRIDLOCK, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Please include full name, address, day and evening phone numbers.