From the Wasatch Choices 2040: "One quarter of people want to ABLE to use transit". Just did a quick estimate for Salt Lake County, and the proportion of the population within a half mile of TRAX. It was about ten percent of the county population. Thus, to match the desire demand, we need an enormous number of new houses in proximity to TRAX.
Now, that makes the logical jump that everyone who wants to be able to ride transit lives within a half mile to TRAX. That makes a certain amount of sense. I now live more than a mile from TRAX, and I never walk to TRAX. I also recently remeasured my daily walk to TRAX from my parents house, and it was far shorter than I had expected--about 2/3 of a mile, not the mile I had expected.