A General Electric subsidiary has dropped its appeal of a federal court order barring a massive shipment of tar sands oil-field equipment from being trucked along a scenic Idaho roadway that cuts through the Indian homelands of the Nez Perce Tribe.

The company's legal capitulation was hailed by tribal officials and environmental groups as a major victory in their three-year struggle against so-called megaload transports, a dispute at the forefront of a larger battle over oil and gas development in North America.

A federal judge issued an injunction last month blocking a planned shipment along U.S. Highway 12 of an oversized water-treatment system bound for delivery by an Oregon hauling company to the tar sands production fields of Alberta, Canada.

The winding mountain road hugs the banks of two federally protected rivers through north-central Idaho and crosses national forest lands following an historic trail broken by early Nez Perce bison hunters.

It also follows the route taken at the dawn of the 19th-century by Meriwether Lewis and William Clark on their famed government-sponsored expedition to chart newly purchased Western territories.

The General Electric affiliate said in a statement on Friday it was abandoning its court fight over the road to focus on other shipment options "due to ongoing uncertainty regarding timely delivery" of its oil-field equipment.

The Nez Perce in August formed a human chain across the two-lane highway in a protest that slowed but did not stop an initial shipment of water purification units owned by the GE subsidiary Resources Conservation Company International.

A second scheduled shipment was blocked in September by the judge, who ordered further megaloads banned along the 100-mile (161-km) route until the U.S. Forest Service studied the environmental, economic and tribal impacts.

Tribal leaders and environmental activists have argued that the scenic mountain road should not be turned into an industrial corridor by international oil companies seeking a short cut to transport outsized equipment from the Port of Lewiston in Idaho to Canada.

The GE subsidiary countered that it stood to lose millions of dollars if its shipments were delayed, according to an appeal of the court order. That appeal was formally withdrawn on Thursday.

"(This) is a significant step forward for not only the Nez Perce people but all persons who believe this special area should not be transformed into something it was never intended to be," Silas Whitman, tribal chairman, said in a statement.

ExxonMobil two years ago dropped plans to ship tar sands equipment on colossal rigs along U.S. Highway 12 after delays tied to a lawsuit by the environmental group Idaho Rivers United. Ultimately, ExxonMobil downsized the loads and used alternative routes through Idaho to Canada.

Conservationists said the legal victories would help protect the scenic river canyon.

"Industrialization of one of America's first wild and scenic river canyons is not acceptable, and the courts have agreed with us," Idaho Rivers United Conservation Director Kevin Lewis said.