A new U.S. Transportation Department report shows the total amount of for-hire freight moved in the country fell 0.6% in September from the month before, the second consecutive monthly drop.

The department’s Freight Transportation Services Index (TSI), which consists of data from for-hire trucking, rail, inland waterways, pipelines and air freight, registered 121.5, 2.6% below the all-time high level of 124.7 in July 2016. These two months of decreases followed four consecutive monthly gains and puts the measure at its lowest level since March.

The August index was revised down slightly to 122.2 from 122.3 in last month’s release while the July reading was revised up slightly to 124.7 from 124.5. When September is compared to the same time a year earlier the reading is down 0.6%

The Freight TSI measures the month-to-month changes in freight shipments by mode of transportation in tons and ton-miles, which are combined into one index.

The September Freight TSI fell due to declines in trucking, pipeline and rail intermodal, while air freight, water, and rail carloads rose, according to the department, which added this took place as the economy was relatively stable.

The 0.7% third quarter decrease matched slow growth in industrial production, which remained unchanged in the third quarter, while gross domestic product growth jumped up to 2.9% in the third quarter, according to the department. GDP growth in the second and third quarters outpaced the 1.5% growth of TSI over those two quarters, after two earlier quarters when GDP grew less than 1% and TSI declined.

Also, the third quarter decrease of 0.7% followed an increase of 2.3% in the previous quarter, for a net increase of 1.5% over the six months. Since the beginning of 2015 the Freight TSI has declined in five out of seven quarters.

The index remains high compared to earlier years, rising 28.2% since the low of 94.7 in April 2009. Freight shipments are up 9.1% in the five years from the post-recession level of September 2011 and are up 7.6% in the 10 years from September 2006.