Driving is declining. Reports like this recent one by USPIRG claim that "The Driving Boom—a six decade-long period of steady increases in per-capita driving in the United States—is over." The US Department of Transportation reported that these trends are continuing, and there was an additional decline of 1.5% in vehicle miles traveled year over year in March. While it is clear that driving is declining, it is less clear why this is happening. Common ideas as to why personal travel is declining in the US include land use changes, transit investment, smart phones and environmental concerns. These may or may not be accurate ideas (I'm skeptical.). This recent report from UCLA suggests that economic factors play a larger role in shifting driving behaviors for young adults.
Only focusing on the decline in driving in the US paints an incomplete picture of associations and policy interventions that may (or may not) have encouraged the shift. I am not convinced that local policies have much to do with the decline in driving in large part because the decline in driving is global (at least in developed nations). Here are data from the UK showing the same kind of decline, and here is a story about research published a couple of years ago covering eight countries. Car companies in Japan have been worried about young people turning away from cars for years, and youth attitudes showing declining interest in driving have been fairly consistent over the past few years. Since these trends are global we should first consider globally shared conditions for explanations as to why travel is going down. Historically high rates of unemployment among young adults is good place to start. Local policy is too heterogeneous to account for overall decline.