May and June reports from the American Trucking Associations’ provide some unfortunate evidence that a national economic recovery is slowing.

The for-hire truck tonnage index in June dipped 1.4%, and the May index decline was revised up from 0.6% to just 0.1%. However, the ATA said May and June marked the first back-to-back contractions since March and April 2009. The latest reduction lowered the SA index from 110.1 (2000=100) in May to 108.5 in June.

According to the ATA, trucking serves as a barometer of the U.S. economy, representing nearly 68% of tonnage carried in 2008 by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 8.8 billion tons of freight in 2009. Motor carriers collected $544.4 billion, or 81.9%, of total revenue earned by all transport modes.

The good news is that total tonnage is up compared to 2009. Compared with June 2009, tonnage climbed 7.6%, which was just below May’s 7.7% increase and the seventh consecutive year-over-year gain. Year-to-date, tonnage is up 6.6% compared with the same period in 2009.

ATA Chief Economist Bob Costello said the May and June reports reflect an economy that is slowing. He said truck tonnage growth is likely to moderate in the months ahead as the economy decelerates and year-over-year comparisons become more difficult.

Costello said the trucking sector has removed so many trucks, trailers and other equipment out of the network that even a slight tonnage growth will be helpful.

“Due to supply tightness in the market, any tonnage growth feels significantly better for fleets than one might expect,” Costello explained.

Michael Tilley with our content partner, The City Wire, has more in this report.