Dear Dr. Gridlock:

What are those machine-gun-toting cops on Metro going to do with those guns?

Seems to me that automatic high-powered weapons in a mass transit system are pretty dangerous. I don't get warm fuzzies when I see big guns amongst thousands of commuters in close quarters.

Can they shoot terrorists without hitting us?

Ken Hill

Centreville

"We think that officers with machine guns serve as a deterrent to would-be terrorists and other criminals," says Metro's spokeswoman, Lisa Farbstein.

Beyond that, their presence tells us that increased security is in place and we all should be alert. The guns could make a terrorist think twice, but Dr. Gridlock sees them more as a symbol of vigilance.

As to whether these trained officers "can actually shoot terrorists without hitting us," let's hope we never find out.

Construction Workers Not Exempt

Dear Dr. Gridlock:

I'd like to know why construction workers in the District are exempt from parking regulations. There is a building being renovated on Maryland Avenue SW, between Seventh and Sixth streets.

The construction crews have removed parking meters and fenced off the curb lane on over half that block. They park their cars there, moving the fences to enter and exit their own private parking lot. What gives them the right to commandeer a lane of traffic for free parking?

Anne Flowers

Fairfax City

Nothing. This goes on all the time, although it is a violation of city rules. Crews can use the curb lane for deliveries and equipment staging areas but not to park their vehicles, according to Bill Rice, spokesman for the D.C. Department of Transportation. He sent some inspectors to the site you mentioned, and DDOT issued a $300 citation for illegal parking.

I looked across the D.C. skyline recently and counted nine cranes. There's plenty of building going on. Workers at these construction sites should not be playing with chain link fences for their commuting benefits. If you see such a site, notify the city at 202-727-1000 and Dr. Gridlock.

P.S. The city requires the contractors to remove parking meters to protect them during construction. The contractor is required to cover the lost meter revenue.

Solution for Saturday Jams

Dear Dr. Gridlock:

Interstate 66 outside the Beltway is constantly backed up on weekends, as everyone is out running errands, heading to youth athletic events or other family travel.

Why doesn't VDOT open the HOV shoulder lanes on the weekends? After all, if their goal is to open them during times of high traffic, the weekend certainly should rank up there.

Thuy Dinh

Arlington

VDOT doesn't think the number of shared rides -- HOV-2 on Interstate 66 or HOV-3 on Interstate 95/Interstate 395 -- would justify HOV use on weekends, according to Ryan Hall, a VDOT spokesman.

I-66 outside the Beltway would be a good place to test this theory, as it does not have reversible lanes, like I-95/I-395. I'd like to see them give it a try.

License Plates Front and Rear

Dear Dr. Gridlock:

A few years ago, I bought a new car at a Prince George's dealership. On taking possession, I noticed there was only a rear license plate, but the salesman assured me that no front plate was needed because of a "new Maryland law."

I drove with the rear plate alone for two years before being ticketed by Virginia police near Pentagon City. When I complained to the Maryland MVA about not notifying Virginia of the "new law," the lady said there was no such thing.

"I bet I know what happened," she said and sent a guard to unscrew my rear plates. Sure enough, there were two plates there stuck together, which the dealership had been too lazy to separate. A sympathetic Arlington judge dropped the charges, but it cost me a day's time to straighten this out.

Rudy Weiss

Bowie

Lesson learned: Maryland, the District and Virginia require license plates front and rear. Shame on that dealer.

Transportation researcher Diane Mattingly contributed to this column.

You can write to Dr. Gridlock at 1150 15th St. NW, Washington, D.C. 20071. He prefers e-mails at drgridlock@washpost.com or faxes at 703-352-3908. Include your full name, town, county and day and evening telephone numbers. Dr. Gridlock cannot take phone calls.