C Burger in the comments mentions this Brookings Institute study that says Vehicle-Miles-Travelled (VMT) by driving plateaued in 2004 and has fallen since. The decline is likely caused by urbanization and by rising gas prices.
In the accompaning video, Brooking’s Fellow Robert Puentes has policy some policy advice:


The advice is essentially, “raise the gas tax and build transit”.

No where is the decline more obvious than New York City. There, population and jobs have been going up while driving has been going down. Subways, trains and buses in New York have absorbed not just all the new growth, but all of the decline in traffic. You can find a more detailed discussion of this phenomenom in New York City over at streetsblog. Now, I would be willing to bet that’s why we’ve been seeing massive increases in ridership for Metro as well.