Annualized turnover rates at large and small truckload fleets fell by 12 percentage points in the first quarter of 2015, according to American Trucking Associations’ chief economist Bob Costello.

Turnover at fleets with more than $30 million in revenue fell below 84%, the lowest it has been since the second quarter of 2011 and the first time it has been below 90% since then. For fleets with less than $30 million in revenue, the turnover rate dropped to 83%.

"Clearly, the decline in driver turnover in the first quarter was significant," Costello said, "but what is less clear is why it dropped so much and whether turnover will continue to remain low."

In the same period, turnover at less-than-truckload fleets fell a single percentage point to 9% which is the lowest level since the second quarter of 2013.

"Drivers continue to be in high demand, so we still see the risks posed to the economy and our industry by the shortage of drivers," Costello said. "The drop in turnover was likely, at least partially, connected to a temporary slowdown in freight movements in the quarter, as well as improved retention efforts of fleets across the board – but I would not be surprised if turnover edges higher in the quarters ahead."

Corrected 11:25 EDT 7/15/2015 to indicate the rate dropped by 12 percentage points, not by 12 percent.