In March, the nation's trucks hauled almost 4% more tonnage around the country than they did a year ago. This is good evidence of the increased physical size of the economy and its continued overall growth.
The top chart shows the long-term trend in truck tonnage and how it correlates to the level of the S&P 500. If anything, it lends credibility to the rise in equity prices, since it shows that equities have risen pretty much in line with the expansion of the economy in the past four years. The second chart shows just the truck tonnage index, and how -- with the exception of a burst of activity in late 2011 and a weather-related drop in October of last year -- the recovery has been relatively steady and constant for the past four years, increasing at a 5% annualized pace since March 2009.