With parks, stadiums and other wide open spaces prohibiting secondhand smoke, the nearly airtight quarters inside an automobile may be the next no-smoking venue.

A bill similar to failed legislation proposed last year to ban smoking in cars occupied by children under age 5 has been filed for the 2008 Legislature to consider beginning in January. Official discussion of the yet unnumbered bill is to begin next week on Capitol Hill. The controversy is already under way.

Proponents say both medical research and common sense warrants the ban. Opponents say it's another in the proliferation of child protection legislation around the country that, simply put, just goes too far.

Smoke-filled cars in parking lots or waiting at stoplights are apparently being noticed, say state Department of Health tobacco-use prevention advocates, who note phone calls mentioning cars are coming almost daily to the agency's anti-smoking hotlines.

One caller who didn't leave a name said he was in a grocery-store parking lot when he noticed a car "so thick with smoke you couldn't see inside. I joked to my wife, 'Well, I guess that's one way to get the most out of your habit. But then I noticed a car seat and a little round head in the back seat. It wasn't so funny anymore."

The situation is the opposite of funny; it's hazardous, said ban sponsor Scott McCoy, D-Salt Lake. It's bad enough for the adult who chooses to smoke to sit in it, but a child strapped into a car seat has no choice whatsoever.

"The car is the smallest, most confined space that people occupy," he said, adding it's more than a little ironic that a parent would care enough about a child's safety to buckle them in, then subject them to such a harmful environment.

Studies have shown that 4,000 chemical compounds are created when a cigarette — paper wrapper included — is burned, and 40 of those compounds are known carcinogens. According to the U.S. Surgeon General, secondhand smoke is particularly harmful to children and increases the risk of sudden infant death syndrome, serious respiratory problems, asthma attacks and middle ear infections.

More than two dozen cities nationwide have approved ordinances banning smoking in cars with minors. At least a half dozen states have legislation pending, with some wanting smoking prohibited with minors in the car younger than 16.

Renn Greenwood, an "at least a pack-a-day" smoker who lives in Sugar House, said he is a little disappointed but hardly surprised that the "smoking police" have another target.

"Every smoker — and I mean every smoker — I know never smokes in a car with the windows rolled up," he said. "The windows are down and the car is moving. Even smokers hate the smell of secondhand smoke, believe it or not. That's why they hold the cigarette outside the car at stoplights."