Adding a new freeway will never reduce pollution, because that does not reduce vehicle miles traveled. Vehicle miles traveled generate half the air pollution in SLCo. Adding more miles traveled will not help.
Our air quality fails twice yearly: pm2.5 (winter) and ozone (summer). We are in "Serious Non-attainment". Which means we may lose all Federal funding for me roads. (The feds pay for 80 percent of new freeways.) Only California and Phoenix are in similar circumstances. Note that both, after decades of freeway expansion, are now engaged in huge programs of transit construction. This suggests the same will occur in Utah.
It is unlikely freeway construction will stop. But it is likely that what will be built will not be grade separated freeway. Rather, the most expensive part of new freeways (interchanges) will be omitted or delayed. Hence, most new roads will be more like Bangerter highway, with innovative intersections rather than interchanges.
Alternately, more like Mountainview corridor: phased segments and widths. A sort of boulevard treatment for a freeway. First, the access lanes (frontage roads) get built (as minor arterials) with a big space left in the middle. And then the freeway lanes in the middle get built.
In any case, the 'surge' of additional mobility historically generated by a new freeway is likely gone for good. And hence the massive profits from developing farmland. The land value uplift will still take place, but at a slower and more gradual rate.
The market knows this, even if it doesn't know it knows. The price of 'raw land' in the county, (even marginal and difficult to develop land) is rising like mad. And housing pricing reflects this. New houses typically cost 5x the cost of the land. So as land prices rise, either new houses get more expensive, or lot sizes fall. I think we see both happening.