The American Trucking Associations' advanced seasonally adjusted for-hire Truck Tonnage Index dropped for a second consecutive month after a year-end run-up.
The index fell 3.2 percent in March, following a revised 3.6 percent decline in February. The index had risen from September 2005 to January 2006.
The index fell to 110.1, its lowest level since November 2003, and 2.6 percent lower than March 2005.
It was the first time since 2001 that tonnage declined on a year-over-year basis for three consecutive months. Volumes generally were weaker than normal during the first part of March but rebounded by month's end and remained strong through early April.
The index based year is 2000, when it was 100.