A 0.6% decrease in the American Trucking Assns.’ truck tonnage index for May was the first month-to-month drop since Feb., but “it’s not significant,” according to industry analyst Noel Perry of FTR Associates.

“It’s normal during an economic recovery to have a few drops,” Perry told Fleet Owner, who pointed out that the May numbers probably reflected the wind down of Federal economic stimulus spending. “It takes three months to establish a trend. One month does not establish a trend. But if you’re asking a month from now (about another decrease), then I’d begin to be concerned.”

While the May seasonally adjusted ATA index showed a decline from April, it was still 7.2% above last year’s May numbers and was the sixth consecutive year-over-year gain, according to ATA. Year-to-date, the tonnage idex is up 6.2% compared to the first five months of 2009.

“Despite the month-to-month drop in May, the trend line is still solid,” said ATA chief economist Bob Costello. “There is no way that freight can increase every month, and we should expect periodic decreases. This doesn’t take away from the fact that freight volumes are quite good, especially considering the reduction in truck supply over the last couple of years.”

But the May tonnage numbers do hold a significant message, according to Perry. “All economists have been forecasting a slow recovery, and despite stronger numbers earlier in the year, the indicators are telling us that a slow recovery is happening,” he said.

Capacity shortages forecast by FTR are based on a slow recovery and are unchanged by the May freight numbers, Perry said.