Julio G. makes the case that Austin's general transit ridership is stagnating and that population decline in the most transit productive areas is to blame. Part of that comes from NIMBYs and a restrictive development code. But I would also argue that transit ridership is on the decline because the most productive destination for transit is declining in share as well.
Employment drives a large percentage of transit ridership and Austin is likely to be no different. 16% of all trips are by transit, but 34% of transit trips (p5) are work trips. APTA on board surveys have put that number around 59%.
So we can't just think of residential, but rather employment in the region. We know Austin has been sprawling for some time, but let's look at the numbers.
Julio says that for the last 15 years, population has increased 34% in the region. Because data from LED is only available from 2002 on, that leaves us with a 13 year period. But the growth in jobs in that 13 years has been 26% or ~675K to ~852K according to LED data.
But for downtown, which I looked at as West of I-35, North of Barton Springs Road, East of Lamar, and South of MLK employment growth is much smaller. Only an 18% change, from ~112K in 2002 to ~132K in 2011. The share of employment that resides in this downtown sector has gone down too. In 2002 it was 16.5% of total jobs in the region, while in 2011 it was 15.5% of total jobs.
1% isn't huge, but its enough to show that employment sprawl is a big issue. And if you depend on employment to drive transit ridership, and your #1 market is losing share, it gets hard to serve.
So in addition to getting more housing in Austin's core, I would argue that for VMT reduction, getting employment into the core is just as important. Right now people are driving to Round Rock or 360 or many other places. Create centers, serve them with good transit, and the ridership will grow.
Obviously easier said than done.
15 Year Population Change
12 Year Employment Change
Regional Jobs - 675K
Downtown Jobs - 112K
Downtown Share - 16.5%
Regional Jobs - 852K
Downtown Jobs - 132K
Downtown Share - 15.5%