The American Trucking Associations has reported that the churn rate at large and small fleets dropped by double digits in the fourth quarter of 2016, thanks only to the choppiness of the freight market.

The driver turnover rate at large truckload fleets sunk 10 percentage points to an annualized rate of 71%, the lowest point in six years. At smaller fleets, driver turnover also fell to five-year lows, dropping by 16 points to 64%.

The turnover rate at large carriers with more than $30 million in revenue has seen a decline for four straight months. The turnover rate at less-than-truckload fleets dipped one point to 8%, marking its lowest level since the first quarter of 2016.

“Continued declines in turnover rate reflects the overall choppiness of the freight market,” said Bob Costello, ATA chief economist. “As inventory levels throughout the supply chain are drawn down to more normal levels, and freight volumes recover, we should see turnover rise along with concerns about the driver shortage.”