Herb Caen liked to write about how the fog snuck into San Francisco on little cat’s feet.

That’s not the case here in Manteca. If you can compare tule fog with anything in the cat family it wouldn’t be the delicate feet of a domesticated purring machine. The analogy would be more like a pouncing saber-toothed tiger.

Wednesday was a classic example. It was clear out until about 9 a.m. when more fog than MTV uses in a decade suddenly masked everything more than three car lengths away.

If you’re not familiar with living through a fog season in the Central Valley, life in the dead of winter isn’t measured in time or miles. It’s car length. Chicago has its chill factor. Los Angeles its ultraviolet scale. We have a refrigerator dial.

And if you want to describe to someone who has never experienced living in the world’s largest cloud that stretches from Redding to Bakersfield between the Sierra and the Coastal Range, tell them it is like being stuck inside a refrigerator for three weeks or so at a time.

Fog, of course, makes people do crazy and stupid things. Drivers decide that if you can’t see it, it can’t hurt you.

Over the years you collect a lot of Central Valley stories about drivers who are in a bigger fog when it comes to logical thinking than there is fog outside their two-ton projectile.

• A man driving 10 miles above the 35 mph speed limit in zero visibility after dark misjudged the location of a turn and ended up on the porch of a home.

• A teen boy became so disorientated in a “white-out effect” after sunrise that he drove his motorcycle into the side of a parked semi-truck.

• Another male driver  who was having a hard time finding his rural driveway in a combination of thick fog and darkness decided high beams would do the trick. The end result was a slow, deliberate turn into a drainage ditch.

The guys were all lucky. They didn’t sustain any injuries or create a lot of property damage. That’s not the case with others whose idea of a safe distance between vehicles would get a chaperoned boy and girl in trouble in most Middle East countries.

One would think after a century of driving in tule fog, that humans would realize that they should take the foot off the gas pedal, keep eyes peeled, radios off and lights on low beam at night whenever they see more gray than at an old mare farm.

But, alas, year after year of massive fog pile-ups show that people aren’t heeding Caltrans and CHP warnings about fog driving tips.

So without further adieu, here’s a stab at increasing the level of competence of drivers in low visibility by taking the “The Manteca Living in  Fog Test.”

1. When low visibility warnings flash up on the high-tech Caltrans fog warning message boards along the Highway 120 Bypass and Interstate 5 you should:

a) Speed up.

b) Ignore them.

c) Close the distance between you and the gasoline tanker ahead of you.

e) All of the above.

2. The reason you want to flip on high beams in zero visibility is:

a) to create a pleasant blinding light effect so oncoming drivers will know if they come toward it they may get to experience the light people say they see when they are hovering on the edge of death.

b) to conduct a field test about the theory that water particles in clouds reflect light back toward you.

c) it makes it easier for oncoming truck drivers to be drawn to you much like a moth is to a porch light.

d) to bounce enough light back into the interior of your car so you can read a magazine while driving down the road at 55 mph.

3. If you are driving in thick fog down the freeway and the truck in front of you is going either 20 mph or completely stopped you should assume:

a) it is completely safe to swing around them at 65 mph.

b) that the guy is simply startled that it has suddenly become clear so you should step on the accelerator and pass without hesitation.

c) that it is OK, since he is moving so slow, to get close enough that you can read all of his license plate tags.

d) that it’s just an optical illusion and not slow down.

Of course, you could just chuck the test and head to San Francisco, which actually makes millions if not billions of dollars a year using fog as a way to lure tourists to The City. You will discover that San Francisco is as clear as a bell this time of year. That natural abnormality is what prompted Mark Twain to say the coldest winter he ever spent was a summer in San Francisco.

Twain may have had something witty to say about Manteca when he passed in this general vicinity heading from San Francisco via Stockton on the old stage coach route that went along French Camp Road to the southern mines, but he probably did so in winter which means he couldn’t see a thing a wagon-length ahead of him.