If you're one of those people who hears on the radio as you're driving to work that it's a "no-drive" day, you're not alone.

The most recent Utah Department of Transportation statistics show that there were a few more vehicles on the road during no-drive days this month than other days.During July 6-13, which were regular driving days, 21 UDOT traffic monitoring stations throughout the Salt Lake Valley showed a total of 41,447 vehicles.

During the no-drive days of July 14-21, those same stations clocked a total of 42,930 vehicles.

"The stations which were used actually showed a little more driving," said Jeanne Shaw, UDOT information specialist.

The Utah Transit Authority doesn't have any statistics for those particular days because it uses a system of random counting, according to Coralie Alder, UTA manager of community relations. Phone calls for bus information - which can be an indication of new ridership - seemed unchanged during those times.

Unlike the "no-burn" days, which carry the weight of law and can be enforced, the "no-drive" days are purely voluntary.

Carol Sisco, spokeswoman for the state Department of Environmental Quality, said that department has no way of measuring the effectiveness of no-drive days.

"We see them as a public education tool, a way of raising awareness that cars cause about 50 percent of the pollution along the Wasatch Front," she said.

DEQ officials determine when to declare "no-drive" days in Weber, Davis, Salt Lake and Utah counties by checking air quality at DEQ stations in the area as well as doing readings by computer.

"They look at the pollution on a given afternoon and the forecasts on a given day. Based on that, they determine whether the next day should be a `no-drive day,' " Sisco said. "The same data also produces the health advisories."

"No-drive" days are mentioned on television weather forecasts but do not receive the same media attention as "no-burn" days.

The DEQ started the "no-drive" day program the summer of 1994 and the first "no-drive" day was July 27 of that year.

Sisco personally has tried to stay out of the driver's seat for the 12 "no-drive" days declared this summer, but she admits it's tough.

And she sympathizes with people who cannot refrain from driving.

"We know that people can't do it every day - it's impossible - but we encourage people to try. If you can avoid driving and you can take a bus or car pool, that's wonderful. If you can't do that, you can help in other days," Sisco said.

Even little things can can make a difference.

For example, people can try to drive less.

"If you go to work in the morning, don't run a bunch of errands during the noon hour. Do them on the way home. You also can avoid using other small engines powered by gasoline like lawn mowers and leaf blowers," she said.

"Even things like not filling up the gas tank until late in the evening can help," Sisco said.

"The emissions that come out of the gas pump as you pump gas contribute to the ozone," she said. "Ozone is formed in the presence of heat and sunlight."

Sisco said the "no-drive" day program is expected to stay voluntary.

"A lot of things to control summer smog have been done. Cars are cleaner, there's no longer lead in gasoline, industry has made all kinds of cleanups. There's not a whole lot more you can do and as the population grows, you're getting more cars on the road," she said.