Austin is one of the fastest-growing metro areas in the country. Over the last five years, the population in the city limits has increased by nearly a 100,000 people, an 11 percent increase. In the larger region, the growth is even greater. But there’s one part of the city that isn’t growing: transit ridership. Let's take a look at what's behind that trend, in the first of a two-part series on transit use in Austin.