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Ravell Call, Deseret News
An inversion covers downtown Salt Lake City on Wednesday, Jan. 9, 2013.

SALT LAKE CITY — During this month's inversion that hung around for more than a week, state Department of Environmental Quality employees and clean air advocates observed something noticeably less frequent: bad air alerts posted on overhead freeway signs.

With another inversion ramping up and no relief expected until at least sometime next week, the worry is that the right message won't get across to motorists to curtail driving on bad air days.

“To see it evaporate just like that when it is so simple and costs absolutely nothing” is worrisome, said Dr. Brian Moench, president of Utah Physicians for a Healthy Environment.

“We have our own suspicions. … It certainly undermines our confidence in state government,” Moench said.

The issue came up during a Tuesday meeting of environmental activists and DEQ staff. Some agency employees said they had noticed the warnings had been posted with decreased frequency or not at all during the inversion that finally broke loose with last Thursday's monster snowstorm.

Both the DEQ and the Utah Department of Transportation participate in the virtual messaging system, or electronic roadway sign alerts, to advise commuters of bad air days and to refrain from driving, if possible.

Nile Easton, UDOT spokesman, said there's been no concerted effort to “downsize” the frequency of those messages.

“We put them up in the initial blast of the inversion, but we don't leave them up. We're afraid people will start to ignore the signs,” Easton said.

He added that traffic center operators follow strict protocols about the duration of messages and the manner of those messages so motorists can count on timely information and will not dismiss what's on the signs.

“We have people wanting to post marriage proposals. … But if DEQ feels we should have those messages up with more frequency, we would be open to that and would love to have that discussion,” Easton said.

One DEQ employee said there was a bad air warning on signs over I-215, but another said they were absent on Legacy Parkway.

On Tuesday's commute, with air quality to the point that wood burning is banned in Davis County, no signs warned of increasing pollution.

Amanda Smith, executive director of DEQ, said the agency wants to come up with a better messaging system, noting that some people have criticized the irony of putting up “reduce driving” messages over interstates.

Still, rough numbers from UDOT show that the boards are effective, reducing vehicle miles traveled by about 6 percent.

Cherise Udell, with Utah Moms for Clean Air, said irony or not, it is the results that count.

“Why take away or reduce something that is working? If it makes you feel guilty when you pass by the sign, then rightfully so. Feel guilty," Udell said. "Ultimately, even if we don't have the signs, you can see the bad air and you can smell it.”

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