DOT Federal Highway Administration released its Traffic Volume Report for March 2014. It shows a very slight increase in total miles vs March '13, though this year was likely to be impacted by severe weather, so growth is anticipated in April. This is confirmed by the EIA weekly reports of gasoline supplied, which have shown solid growth in each of the last 11 weeks, save one. Combined with the long term trend in improving fuel efficiency, this suggests traffic is generally growing.
DOT Traffic Volume:
EIA Gasoline Supplied: