Tons of pollution generated by cars on the freeways would be greatly reduced by driving at 55 mph instead of 65 or 75 mph. I've calculated that it would take less than 3 extra minutes to drive a trip from the 106th South onramp to the 6th South offramp, about 15 miles.
Similar trips on other stretches of freeway would take little extra time, with significant savings in air pollution generated, possibly fewer accidents or lesser ones, and lower gasoline consumption.
We have a current traffic system in place, regulating speed in Parleys Canyon, reducing speeds when bad weather conditions exist.
Why not use regulatory signs above the valley freeways to reduce the speed on red air quality days? Think of the significant results while taking so little extra time.
Salt Lake City