Dear Dr. Gridlock:

On Rock Creek Parkway this morning, southbound traffic suddenly slowed to a crawl between the Connecticut Avenue and P Street exits. The rare rush-hour backup on Rock Creek is usually attributable to a broken-down car that can't get off the road, but today's slowdown was because of a cyclist who was on the parkway rather than on the bike path.

I understand the need to share most roads with cyclists, but it seems absolutely ridiculous (not to mention rude and a little insane) for a cyclist to use Rock Creek Parkway -- a relatively high-speed, curvy road -- when a safe path is available right next to it.

I'm curious about the law here, as well as your take on this from a safety and driving ethics perspective.

Amy Levin

Washington

Bicyclists are entitled to use a lane of traffic, as are operators of motor vehicles. However, the situation you describe sounds dangerous for the bicyclist. The driver of a motor vehicle coming around a curve may not see the bicyclist in time to stop.

Of course, motorists should be more careful, and should share the road, but that will be of little consequence to a flattened bicyclist.

Double-Parkers Moved

Dear Dr. Gridlock:

The bottleneck on 18th Street NW between M Street and Connecticut Avenue, caused by double-parked cars and trucks on 18th Street, has created havoc daily for commuters. Well -- for the time being, anyway -- the police have taken notice and have been present each day this week as I have passed by that block at around 4:45 pm.

Looks like e-mails to the mayor as well as comments to Chief Charles Ramsey during his online discussions at washingtonpost.com regarding this problem have paid off! Let's hope it lasts!

Thanks to both of them for reacting and to you for your terrific column.

Bob Henkel

Washington

I do hope police are turning their attention toward chronic downtown bottlenecks caused by illegal parking. Eighteenth, 19th and 23rd streets, and H and I streets -- all in the downtown business area -- are places where illegal parkers take away a lane of traffic, causing significant backups.

Signal of Politeness

Dear Dr. Gridlock:

I drive on the Beltway toward Tysons every morning, and I've seen this a million times: A driver signals to change lanes, and the driver in the other lane speeds up to prevent it.

It infuriates me every time I see it. If I see someone signal, I make it a point to give him room to merge.

Debra Cook

Burke

Transportation researcher Diane Mattingly contributed to this column.

Dr. Gridlock appears Sunday in the Metro section and Thursday in Extra. You can write to Dr. Gridlock, 1150 15th St. NW, Washington, D.C. 20071. He prefers to receive e-mail, at drgridlock@washpost.com, or faxes, at 703-352-3908. Please include your full name, town, county and day and evening phone numbers.