The American Trucking Associations'(ATA)  advanced seasonally adjusted truck tonnage index rose 3.3% in 2019, marking the index's 10th straight annual increase, ATA said Tuesday.

Despite the gains, the 2019 increase was half the growth rate seen in 2018, officials said. The index rose 4% in December after falling a revised 3.4% in November, officials also said.

"Last year was not a terrible year for for-hire truck tonnage, and despite the increase at the end of the year, 2019 was very uneven for the industry," ATA Chief Economist Bob Costello said in a statement. "The overall annual gain masks the very choppy freight environment throughout the year, which made the market feel worse for many fleets. In December, strong housing starts helped advance the index forward."

ATA's tonnage data is dominated by contract freight. The association calculates the tonnage index based on regular monthly surveys of its membership.