gramarye said:
My problem is that there are two primary reasons people might switch to public transportation and away from cars. One sends a good message and one sends the opposite.
If people are leaving their cars and taking the bus/train/bike because their lifestyle has become more amenable to it, their cities have diversified their transportation infrastructure portfolios, and they've overcome the social stigma regarding people who take public transit, that's good.
If more people are leaving their cars because they can't afford the significant expense of maintaining one (or two, or three), either because their income has gone down or because it simply hasn't risen as quickly as the costs of car ownership have, I don't think that sends any particular pro-urbanist message (since it's not a sign of changing attitudes or of better urban planning) and sends a strong negative message about the state of the economy.
If both A and B lead to C, you can't infer A or B from the simple existence of C.
Following your point on income, we must not forget the impacts of high levels of unemployment. Real unemployment has grown tremendously over the past few years. Since most people drive for work, it would make sense to see a decline in driving if less people have to drive to work.
Infrastructure is an important component of making alternative transportation viable. People tend to adopt life-style changes that are "easy" and shun off changes that are "difficult" (unless forced to do so by circumstance). If alternative transportation is perceived as easy, I think more people will migrate towards it, but the infrastructure must be there. Thankfully, cities have been making progress on it.
In regards to the population statistics, do the number account for the flight to the South? So more move in of one demographic and more move out of a demographic thereby changing the demographic compositions of the area? For instance, if 20% of 20-40s moved into an area and 10.5% of 60-80 left the area, the growth would be 9.5%+, but the overall mean age of the city would decline. This could have a huge impact on the values of the city and/or the socioeconomic status of the city (we have all seen great neighborhoods fall down and bad neighborhoods be reborn based on population shifts).