Check this graph out from the Phoenix Metro web site. It shows bus ridership in years past, and more recently both bus and light rail ridership.
You can see a few things. First, note that almost all the rail ridership came at the expense of bus ridership. It was almost a pure 1:1 substitution. The bus ridership, even with a half year of light rail being open, was 65.7 million in 2009. Total ridership was only 67.6 million in 2010 and 2011. Yes there is a recession here, but of the 12 million or so in light rail ridership, at least 10-11 million of that came out of buses. Essentially, we paid $1.4 billion in capital costs to move 10 million riders to a mode of transit that is at least an order of magnitude more expense. Nice work.
Second, note that after over 12 years of growth, with the onset of light rail transit ridership has stagnated for 6 years. Some of this, at least initially, is likely due to the recession but in fact recessions are supposed to spur transit ridership, not reduce it, as people look for lower cost alternatives. There is a good explanation for this. Because light rail is so much more expensive, the cost per rider for the entire transit system has skyrocketed. With budgets unable to be increased this fast (and with fares covering only a tiny percentage of rail costs), the system must cut back somewhere. Since rail can't really be cut back, bus routes are cut.
If we had seen the same growth rate from 2009 to 2014 as we had seen in the twelve years prior, we should have over 86 million trips in 2014 (note these are fiscal years, and fiscal year 2014 is already closed, so this is not partial year data).
We paid, and continue to pay (since rail must be subsidized heavily) billions of dollars to reduce transit ridership.