Dear Dr. Gridlock:

Can you settle an argument between my wife and me over making a left turn at an intersection?

We agree that it is legal to make a left turn at an intersection with a simple stoplight (no left turn arrow) if the light is green and there is a safe gap in the oncoming traffic.

We disagree, however, when the left turn arrow has turned red. I say that it is still legal to make a left turn if the main light is green and there is a safe gap in oncoming traffic.

Why should this situation be any different than in the first case when the stoplight does not have a left turn arrow?

My wife says that the red arrow means that no left turn can be made even if it is safe to do so.

Please explain to my wife why I am correct.

Robert E. Anderson

Falls Church

Your wife is correct. Red on a traffic signal means no. Red arrows are put there because there is high-volume opposing traffic that cannot move safely if you are turning left.

Please memorize the three words that lead to long marriages: "I was wrong."

Seeking Online Input

I was talking last week with Jim Brady, the executive editor of our Web site, www.washingtonpost.com, about how we could further use the Internet to help people with local transportation questions.

We talked about public interest in daily construction delays, the status of major projects, indexing Dr. Gridlock's columns on popular topics, such as teen driving, and alternate routes to New York and Boston that avoid the Interstate 95 corridor.

We also talked about a page that would feature daily updates on traffic backups. (The Web site now offers traffic camera views at www.washingtonpost.com/traffic.)

Jim Brady is a Fairfax County-to-Arlington County commuter. He understands suburban traffic concerns, down to the nanosecond deviations of a particular traffic light on his commute. Finally, we were wondering this: How can we best serve you folks? Do you have some ideas about how our online component can help you in your travels? What instant information do you want?

Please send your responses to executive.editor@washingtonpost.com. And please send a copy to me at drgridlock@washpost.com. Readers are our best resource. Thanks.

Parking Not Just for Riders

I have learned something about parking at Metrorail stations: Even though Metro has spent tens of millions of dollars to provide badly needed additional parking, the new spaces are not reserved for Metro customers. Instead, anyone can park there. And Metro cannot provide any surveys to indicate how many of the new spaces are actually used by Metro customers.

This came to my attention when a Maryland reader complained that construction workers at a nearby federal building were filling up the Suitland Metrorail parking lot, crowding out Metro customers.

I asked Metro spokeswoman Lisa Farbstein about it, and she said that Metro monitors this situation and that outsider parking is "rare."

Several readers disagreed. "I'm not sure how they monitor the parking lot, but obviously not very well," wrote Sandra Williams of Upper Marlboro. "If Metro's parking lot monitors would drive to the top level of the facility EVERY morning between 7:45 and 8 a.m., they would see construction workers park their cars, unpack their equipment and then practically get dressed on the parking lot."

I sent these follow-up letters to Farbstein, and she had a new take: "We do everything we can to encourage Metro passengers to use the Metro lots," she said.

"At the same time," she said, "it is a public parking lot, and it is not breaking any law for someone to park there and not ride Metro."

Hmm. Additional parking is a good thing. We want people to get out of their vehicles and use Metro. However, I wonder how Metro figures out the cost per space for proposed new parking when it has no idea whether the new spaces will be used by Metro customers?

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.