That's a common argument but I really don't think there's much reality to it. A little at the margin, but not much.  Most people leave their homes and go places because they need to.  Good or bad roads or good or bad transit isn't going to keep them (or make them) go where they need/want to go.

And whether they take transit or not is based almost entirely on whether transit is a good fit for where they need to get to/from. (And for the vast majority of people in the metro Denver area, it isn't.)  Which means most people are still going to hit the roads.

The question is whether we're going to have roads that accommodate them well, or roads that are don't (causing more delays and frustration).

Clearly, bad roads have not been a deterrent to keeping people from moving into the Denver area.  Our roads are clogged because tons of people keep moving here.  That's gonna keep happening regardless of whether we have good roads or not.