Tonnage moved by the nation's for-hire truck fleets in April rose 0.9 percent from the tonnage figures reported in March, putting a closely watched index at the highest level since the financial crisis began in September 2008, the American Trucking Associations (ATA) said on May 28.

The ATA's seasonally adjusted index increased in April for the sixth time in the last seven months, according to the group. The April gains raised the seasonally adjusted index to 110.2, with 100 being the baseline. The tonnage index has increased 6.5 percent over the last seven months, ATA said.

Seasonally adjusted tonnage in April climbed 9.4 percent over April 2009 tonnage, the fifth consecutive year-over-year gain and the largest increase since January 2005, ATA said. Year to date, tonnage is up 6.0 percent compared with the same period in 2009, ATA said.

The "not seasonally adjusted" index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 111.3 in April, down 4.4 percent from the previous month, ATA said.

"Truck tonnage volumes continue to improve at a solid, yet sustainable, rate," said ATA chief economist Bob Costello in a statement. Costello added that for most fleets, "freight volumes feel better than reported tonnage" because capacity, especially in the truckload sector, is rapidly tightening.