BOISE, Idaho (AP) -- A federal judge has sided with environmentalists and ruled the U.S. Forest Service erred by not exercising its regulatory authority when the state allowed huge trucks to haul giant oil refinery equipment along U.S. Highway 12.

U.S. District Judge B. Lynn Winmill issued a decision Thursday that handed Idaho Rivers United a victory in the case.

The group sued the government in 2011 after the state allowed ExxonMobil's Canadian unit to ship hundreds of so-called mega-loads from Idaho's Port of Lewiston along the two-lane highway. The roadway runs through a scenic corridor protected by the 1968 Wild and Scenic Rivers Act.

IRU claimed the forest service neglected its duty by not getting involved in the decision-making process.

Winmill agreed, saying the agency has the authority to intervene in such cases.

Copyright 2013 The AP.