Superstorm Sandy helped drive tonnage figures down in October, resulting in the lowest level for the American Trucking Associations' seasonally adjusted For-Hire Truck Tonnage Index since May 2011.

The ATA's SA index dropped by 3.8% in October after falling 0.4% in September. The 0.4% decrease in September was revised from a 0.1% gain previously reported.

October's drop was the third consecutive one, totaling 4.7%. As a result, the SA index equaled 113.7 (2000=100) in October, the lowest level since May 2011. Compared with October 2011, the SA index was off 2.1%, the first year-over-year decrease since November 2009.

Year-to-date, compared with the same period last year, tonnage was up 2.9%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 123.7 in October, which was 7.7% above the previous month.

"Clearly Hurricane Sandy negatively impacted October's tonnage reading," ATA Chief Economist Bob Costello said. "However, it is impossible for us to determine the exact impact."

Costello noted that a large drop in fuel shipments into the affected area likely put downward pressure on October's tonnage level, since fuel is heavy freight, in addition to reductions in other freight.

"I'd expect some positive impact on truck tonnage as the rebuilding starts in the areas impacted by Sandy, although that boost may only be modest in November and December," he said. "Excluding the hurricane impacts, I still think truck tonnage is decelerating along with factory output and consumer spending on tangible-goods."

Peter Nesvold transportation analyst with investment advisory firm Jefferies & Co., noted that excluding October, the current trends in tonnage closely resemble a "typical" truck cycle.

In an email to investors, Nesvold says, "We compared this current tonnage cycle to our truck composite model, which aggregates truck tonnage data over the past 40 years, and we found that this tonnage cycle has been unremarkable in a historical context.

"Based on how devastating the 'Great Recession' was, we expected to see huge swings in truck tonnage relative to the "typical" tonnage cycle. What we found, however, is that this tonnage cycle has been in line with historical trends."