"I'm going to not want to be driving my car, particularly on I-10 with semis and tailgaters all around me. Ten years from now either ADOT will take my license away from me, or I will say, 'Gee, if I could go on public transportation, would that be great!' I'm sort of a stand-in for all those retirees around the state who normally wouldn't think of something like this themselves, and wouldn't have the ability to implement it."
Golf cart retirement communities are one solution, but public transit in relatively dense areas allows older people to still get around after they perhaps shouldn't be driving anymore.
This story is about a potential longer distance project, where I think this is less of an issue, but enhanced mobility for old people is a good reason for mass transit.