Q Recently while driving east on Interstate 205 through Tracy, the fog was very thick and traffic slowed to 35-40 mph. I’m pretty familiar with the rules for driving in fog (obviously, slow down, no brights, don’t tailgate, etc.), but not this.

Ahead we saw a car with its emergency flashers on. We thought the car was disabled, and what a terrible time and place to break down.

But no. The car was traveling less than 30 mph in the fast lane, flashers on. Obviously traffic was forced to go around.

Shortly after that we came upon another car doing the same thing, only fortunately in the slow lane. But again it gave the initial impression of a disabled vehicle. I’m aware of “wipers on, lights on” law. Is there a fog/flashers rule I’m not aware of?

Dan Hendrix

San Jose

A No. There is no fog/flasher requirement, and in fact it can be a one-point moving violation to drive with your emergency lights on. There are only certain circumstances in which you are allowed to use your hazard lights, and driving in fog is definitely not one of them. Check out vehicle Code section 25251(a) for details on when you can use hazard lights.

Driving this way creates a larger problem, because other drivers may mistake emergency lights as a warning that someone is stopped, causing them to brake inappropriately and risking an accident.

The California driver’s handbook says:

“The best advice for driving in the fog is DON’T. You should consider postponing your trip until the fog clears. However, if you must drive, then drive slowly, turn on your windshield wipers, and use your low-beam headlights. The light from the high-beam headlights will reflect back and cause glare. Never drive with just your parking or fog lights.

“Increase your following distance and be prepared to stop within the space you can see ahead. Avoid crossing or passing lanes of traffic unless absolutely necessary. Listen for traffic you cannot see. Use your wipers and defroster as necessary for best vision.

“If the fog becomes so thick that you can barely see, pull completely off the road. Do not continue driving until you can see well. Turn off your headlights and keep your foot off the brake pedal or someone may see your taillights, think you are moving, and drive into your vehicle.”

Q I tried to find the rules for using emergency flashers on the Web but was unsuccessful, so perhaps you could help. I seem to remember a bit in your column about using them to warn other drivers when backing out of a parking space if the view is blocked by another vehicle. Have you run this idea by law enforcement? If so, what reaction did you get?

Toni Harvey

A Here it is, from Greg-the-Traffic-Cop:

Go to www.dmv.ca.gov/pubs/vctop/d12/vc25251.htm and you will see that the law is specific to the roadway and not private property or off-street parking lots. If you are in the Target parking lot and want to drive around with your hazard lights on, there is no violation (we obviously don’t recommend it and you may be mistaken for a security patrol, but there is no violation because it is not on the public roadway).

“For those on-street parking spots where you may have to back out into a lane of traffic and you are worried about whether people can see you because of other parked cars, go ahead and use them. As long as you use them for this limited purpose I think you are fulfilling subsection (3) warning other motorists of a hazard on the roadway. In this case your backing may create a hazard. Just be sure to turn them off as soon as you are done backing up.

“Your readers can find all this information at www.dmv.ca.gov and then typing in their topic on the search bar.”

Q One of my favorite billboards used to be off Highway 101 in Redwood Shores. It was part of a downtown shopping campaign by Redwood City. The slogan was “Redwood City — Palo Alto without the attitude.” OK, maybe not, but I loved them for trying.

David Blinn

A Me, too.

Go to Roadshow’s expanded online presence at www.mercurynews.com/mr-roadshow and look for rules of the road, construction updates and favorite stories. Look for Gary Richards at Facebook.com/mr.roadshow or contact him at mrroadshow@mercurynews.com or 408-920-5335.