Here's the rail ridership numbers for Salt Lake City over the last few years in relation to other cities (generally those with comparable ridership figures).
TRAX
Outside of the mid-2008 spike, ridership has been remarkably steady for TRAX, never dipping below 41,000 nor exceeding 48,000. Sacramento and Saint Louis showed fairly consistent declines, while Phoenix has seen a fairly strong growth trend. Dallas had been trending down, but has since spiked with the addition of a new line there. Minneapolis and Baltimore have seen modest growth trends, while Buffalo, San Jose, and Denver (save for a dramatic drop in one quarter) have been fairly level over the span.
FrontRunner
Starting in the first quarter of 2009, the growth trend has been very good for FrontRunner. Dallas and Seattle have generally been trending downward, while Albuquerque and Oakland have seen growth. Oceanside has generally followed the same trend as SLC.
Data from APTA Ridership Reports