If the Salt Lake City Council is concerned about engine idling and the smog this generates, it ought to be setting aside an idling ordinance and instead do something about the plague of haphazardly timed signal lights. This is where virtually all the idling takes place.
It wasn't nearly this bad in Los Angeles where I grew up. The technology for intelligent traffic control has existed since at least the '60s. Undoubtedly the technology already is in place here in Salt Lake City and requires only a sufficient commitment to intelligent management.
Once this is in effect, then let's consider a reasonable idling ordinance, if necessary.
Salt Lake City