Fluctuating tonnage may prove to be the theme of 2016, as it related to monthly truck tonnage reports issued by the American Trucking Associations (ATA).And December was no exception, with the ATA reporting today that seasonally-adjusted (SA) for-hire truck tonnage for the month at 133.8 (2000=100) was off 6.2 percent compared to November’s 142.7, which was up a revised 8.4 percent (from an original reading of 8.2 percent) over October. The December SA was well below the February’s all-time high of 144.Compared to December 2015, the SA was off 0.7 percent, which paled compared to November’s 5.9 percent annual increase, and SA tonnage for all of 2016 was up 2.5 percent. The ATA’s not seasonally-adjusted (NSA) index, which represents the change in tonnage actually hauled by fleets before any seasonal adjustment for December, was 1.6 percent below November’s 136.1 at 133.9. The NSA was up 0.9 percent compared to December 2015.As defined by the ATA, the NSA index is assembled by adding up all the monthly tonnage data reported by the survey respondents (ATA member carriers) for the latest two months. Then a monthly percent change is calculated and then applied to the index number for the first month.“The ups and downs that plagued most of 2016 continued in December,” said ATA Chief Economist Bob Costello in a statement. “I don’t recall a year in recent memory with so many large swings on a month-to-month basis. Looking ahead, there are some positive signs for truck tonnage. This includes the continued spending by consumers, larger wage gains, and solid home construction. Factory output will continue to be soft, but it should be better this year than last year. And most importantly, the supply chain continues to make progress reducing bloated inventories, which will help truck volumes going forward.”This sentiment has been echoed by many freight transportation stakeholders whom maintain better things are in store for 2017, but that comes with the caveat of sustained volume and GDP growth, buoyed, to a large degree, by strong consumer spending levels. But to what degree these things occur is far from certain.