Dear Dr. Gridlock:

I am absolutely terrified of the Bay Bridge and have managed to avoid it all my life.

However, because of an upcoming family reunion on the Eastern Shore, I have to make that trip.

I don't want to spend one second more on that bridge than I have to, so what are the best times to drive over on a Saturday and return on a Sunday to avoid backups?

If we actually had to STOP on that bridge I think I would DIE. We will be leaving from Burke.

P.S. NO ONE on Earth can be more afraid of that bridge than I am.

Karen Starkey

Burke

The Maryland Transportation Authority considers these the best times to travel over the Bay Bridge to avoid congestion: eastbound, 10 p.m. Friday to 8 a.m. Saturday, and 7 p.m. Saturday to noon on Sunday; westbound, 7 p.m. Saturday to noon Sunday and after 11 p.m. Sunday.

But more useful to you may be this information: Help is available for anyone afraid to drive across the bridge.

With a little notice, the authority will arrange to tow your vehicle across. You can ride in the cab of the tow truck, and if your family requires more space, officials will round up another vehicle. All at no charge.

About 900 people typically use this service between Memorial Day and Labor Day, according to Kelly Melhem, spokeswoman for the authority. The service is offered seven days a week from 6 a.m. to 10 p.m.

She asks that you call 410-974-1622 one hour before arrival. Eastbound drivers looking for a tow should go to the truck weighing station, on the right side just after the toll plaza, and westbound traffic will find the service offered at a small white garage on the bridge approach.

According to Stedman's Medical Dictionary, fear of crossing a bridge has a name: gephyrophobia. Dr. Gridlock would be interested in hearing more about this phobia, especially information about treating it.

Learners Out of State

Dear Dr. Gridlock:

My daughter has a learner's permit in Virginia. We are planning a trip to New England later this summer and hoped that she could do some of the driving.

The AAA tells me that the Virginia learner's permit is not necessarily valid in other states and that we would have to contact each state that we would be driving through.

This seems like valuable information for families. Would it be possible to provide the rules in other states for teens with learner's permits?

Paul Astrow

Springfield

I would love to provide this information for you, but have been unable to find such a list. The motor vehicle departments in Maryland and Virginia also suggest that you contact their counterparts in each state. They also say that what is valid for you in your home state may not be valid in another state.

If anyone can find such a list of driving rules by state, Dr. Gridlock would like to know about it.

Bad Air, Free Transit

Here's a reminder of free transportation. When the regional Council of Governments declares a Code Red day because of unhealthful air pollution, the following bus systems are free:

Arlington Transit, Fairfax Connector, OmniRide, Fairfax CUE, Prince George's County The Bus, Alexandria DASH, Loudoun Commuter Bus, OmniLink, Montgomery County Ride On, and Metrobuses in Northern Virginia and Montgomery and Prince George's counties.

The Air Quality hot line number that provides Code Red information is 202-962-3299.

A Puzzling Plate

Dr. Gridlock received some unforeseen reaction to the answer to the license plate puzzle we ran in last Monday's column.

The puzzle: What kind of car has the license plate 1 DIV 0? About 400 people, including Chief Justice William H. Rehnquist, wrote back that the car must be an Infiniti, since one divided by zero is infinity.

The Doctor endorsed the solution. That was the right car. Mark J. Levin, of Gaithersburg, wrote in to say he was the owner who created the tag to indicate his car was an Infiniti.

But although the solution was right, the math apparently wasn't. It was near gridlock in my e-mailbox last week as mathematicians of all stripes, from a high school teacher to a university professor, pointed out the error.

They came to a unanimous verdict summarized by Paul H. Edelman, professor of mathematics at the University of Minnesota. "With all due respect to the Chief Justice and The Washington Post, 1/0 is undefined, not infinity," Edelman wrote. "It is not a trivial matter to incorporate infinity into a theory of arithmetic."

At Rehnquist's office, his aides said he was amused by the reaction but would not have any comment. That leaves me out there where the air is thin. Apologies to the math purists.

An additional consequence of the column was that when other news organizations picked up the item, they reported, incorrectly, that Rehnquist was the only person to have solved the puzzle or that he was the first to get it right. Wrong on both counts, but that irritated many of the hundreds of people who felt they also deserved credit for figuring out that the car was an Infiniti.

They're right. We should have made it clear that many readers came up with the "correct" answer.

Dr. Gridlock's assistant, Jessica Medinger, contributed to this column.

Dr. Gridlock appears Monday in the Metro section and on Wednesday or Thursday in the Weekly and Extra sections. You can write to Dr. Gridlock, P.O. Box 3467, Fairfax, Va. 22038-3467, or email him at drgridlock@washpost.com. The Doctor's fax number is 703-352-3908. Please include your full name, address and day and evening phone numbers.

Springfield Interchange Update

Tuesday or Wednesday:

1. From 9:30 p.m. to 5 a.m., two right lanes just south of the Interstate 495 ramps leading onto southbound Interstate 95 will be closed near the Commerce Street Bridge for the setting of a barrier wall and pavement marking.

Monday through Thursday:

2. From 9:30 p.m. to 5 a.m., the right lanes will be closed on Amherst Avenue between Bland Street and Springfield Boulevard for bridge construction. One lane will remain open.

3. From 9:30 p.m. to 5 a.m., traffic will be shifted to the eastbound side and one lane will be open in each direction on Old Keene Mill Road between Backlick Road and Loisdale Road for bridge construction.

4. From 9 a.m. to 3:30 p.m. and Friday from 9 a.m. to noon, the left lane in each direction will be closed on South Frontier Drive between Franconia Road and Mall entrance No. 3 for median construction.

Today to winter 2001:

5. The Old Keene Mill Road (Route 644) ramp to southbound I-95 will be closed for the construction of new ramps to both northbound and southbound I-95. VDOT has posted detour signs to send traffic south on Backlick Road for 2.5 miles to enter I-95 at Newington. Motorists also can take Rolling Road south, turn left on Alban Road and drive north for 1A miles until they see signs for I-95.

For updates on lane closures, check www.springfieldinterchange.com or call toll-free 1-877-95-95-222 to reach VDOT information operators.

SOURCE: Virginia Department of Transportation

CAPTION: The Maryland Transportation Authority will tow cars over the bridge.