The amount of for-hire freight moved across multiple transportation modes increased 1% in December from the month before, marking the third consecutive monthly gain, according to the Transportation Department.

This latest reading of the Freight Transportation Services Index (TSI) also ties the all-time high level hit during July 2016 as December shipments increased 2.9 % from the same time a year ago.

The November index was revised upward to 123.5 from 123.2 in last month’s release. Monthly numbers for August through October were also revised up slightly while figures from January through June 2016 were revised down slightly.

The Freight TSI measures the month-to-month changes in for-hire freight shipments by mode of transportation in tons and ton-miles, which are combined into one index and includes the output from trucking, rail, inland waterways, pipelines and air freight.

The December Freight TSI grew due to increases in trucking, pipeline, rail intermodal, and water while air freight and rail carloads declined. According to the department, it was driven by economic growth from increased industrial production during the month along with gains in employment and personal income.

For the final quarter of 2016, the Freight TSI improved 2.9% from the previous quarter’s downturn of 1.1% as growth in the nation’s gross domestic product slowed to an annual pace of 1.9% from 3.5% during the third quarter.

The department noted the fourth quarter slowdown in GDP growth was preceded by a third quarter decline in Freight TSI and the rapid GDP growth in the third quarter was preceded by a strong increase in Freight TSI in the second quarter.

The fourth quarter 2016 Freight TSI increase is the largest gain since the fourth quarter of 2011 and is 1.8% above the level at the beginning of 2015. The index remains high compared to earlier years, rising 31.7% since the low of 94.7 in April 2009.