The American Trucking Associations (ATA) measures the health of motor freight industry using its monthly for-hire truck tonnage index. Based on that benchmark, things are generally going well. The index in 2013 increased 6.2 percent over 2012 results, making 2013 the best year since 1998.

But John G. Larkin, lead transport analyst at Stifel, Nicolaus & Co., uses a different method to take the trucking industry's temperature, and that method produces a more sobering reading. According to Larkin, dry-van truckload shipments have not recovered as strongly as flatbed and refrigerated loads have since the 2008-09 economic downturn. Furthermore, dry-van loads turned negative in January for the first time since April 2013. Larkin presented his findings at the NASSTRAC annual conference in Orlando, Fla., in mid-April.

According to Larkin's data, dry-van load volumes plunged in late 2008 and into the first half of 2009. Van loads shot up again in late 2009 and the beginning of 2010, but since then, they've spent as much, if not more, time in negative territory than in positive terrain.

Van-load activity has been suppressed by improved software tools and processes that allow shippers to better optimize their loads, Larkin said. Persistently sub-par demand has also played a role, he added.

The apparent disconnect between tonnage growth and load stagnation could be attributed to the surge in demand for trucks hauling sand used in oil and gas fracking operations, Larkin said. He noted that movements of such a heavy commodity could skew the tonnage figures without leading to a corresponding rise in loads.