You can see the overall decline in VMT that starts in 2007 after the peak of over three trillion miles. The green line shows urban travel, which stopped increasing and leveled off, and the red is rural travel, which started to decline in 2002. At a glance it seems that much of the decline in overall VMT can be attributed to declines the rural road networks. This does not preclude demographic shifts, but people haven't been moving as much in the US and there hasn't been a dramatic rural to urban migration starting in 2002. Potentially some of the rural decline could be from land getting reclassified from rural to urban, but I don't expect this would be a big effect.
Here is a table that shows the data from the above figure along with the relative changes from peak VMT for rural and urban areas. Where rural VMT has dropped 13% from the 2002 peak, urban VMT has dropped less than one percent from the peak in 2007. That the relative share of VMT has increased in urban areas is just an artifact of the rural decline. Travel reductions are not evenly distributed.
|Rural and Urban Vehicle Miles Traveled in US 2002-2011|
|Rural||Urban||Total||% Rural||% of Rural Peak||% Urban||% of Urban Peak|
Certainly there are changes afoot in the US economy and transportation. This post is not intended to make any dramatic claims about VMT declines. However, these data suggest that the bulk of decline is from rural reductions, not urban reductions. Of course, we need more research about this.