The average marginal cost per mile for 2011 was $1.71, the highest of the four years studied.
The amount of freight carried by the for-hire transportation industry rose 0.1 percent in July from June, rising after a one-month decline.
The index outpaced August 2011 volume by 8.4 percent, the sixth time in 2012 that volume has exceeded prior-year levels.
For-hire trucking companies added 1,400 payroll jobs in August as the overall U.S. economy added 96,000 nonfarm jobs.
Trade using surface transportation between the United States and its North American Free Trade Agreement partners Canada and Mexico was 6.6 percent higher in June than in June 2011.
The TCA is collaborating with Internet Truckstop and Big Truck TV to offer TCA members a twice monthly webcast highlighting truckload-specific economic and industry data
Reading is down from the July index, reflecting ongoing industry concerns over economic, regulatory and political uncertainty.
FTR Associates' Shippers Conditions Index for June basically was unchanged from the previous month and remains in near-neutral territory.
Sign up to get Overdrive's daily newsletter.