Prices have dipped 19 cents in the last past six weeks as a result of an inventory glut caused by a mild winter. Refiners produced more diesel fuel from already-high heating oil supplies.

ATA, meanwhile, is seeking to create a single diesel standard to help eliminate shortages and stabilize pricing. Boutique fuels used in certain parts of the country exacerbate local shortages, the economist said.

The national trucking group also is seeking greater investment in refining capacity.