One of the more interesting traffic analyses that I've run across in a while tracks the number of trips per household by reason and in total. For example, how many trips are now being taken by households for work, shopping, recreation etc. compared to historical patterns? The decline of brick and mortar retail and rise of internet purchasing appear to be making a significant impact - and positively so, at least from the perspective of taking vehicle traffic off the highways.
Source: Energy.Gov Vehicle Technology Office