BOISE, Idaho (AP) — U.S. officials on Wednesday approved two high-voltage transmission line routes in southwestern Idaho aimed at modernizing and improving reliability of the Pacific Northwest's energy grid.

The U.S. Department of the Interior's approval is for the two final segments of the Gateway West project proposed a decade ago by the Idaho Power and Rocky Mountain Power utilities.

The transmission lines "will help power the American West for years to come," Interior Secretary Ryan Zinke said in a statement.

The 1,000-mile project is one side of a triangle of transmission lines supporters have said are needed to meet future regional electricity demand and improve the system's reliability.

Federal officials already approved other segments and work has been completed on three, said Dave Eskelsen, spokesman for Rocky Mountain Power. Work on the section approved Wednesday is tentatively set to begin in 2020 and be completed in 2024.

"This is a major step, of course, but there's still a lot more work to be done," he said.

Approval of the Idaho segments was delayed by landowners who did not want transmission lines on their property and environmentalists who did not want lines in the Morley Nelson Snake River Birds of Prey National Conservation Area, which is protected by federal environmental restrictions.

U.S. Rep. Mike Simpson, R-Idaho, working with conservation groups, in 2017 helped pass through Congress a change in the boundary of the conservation area that allowed the transmission lines to go through. It was signed into law in May by President Donald Trump.

"This Idaho solution is good for the economy, conservation, and ratepayers who will benefit from lower rates and transmission reliability," Simpson said.

The legislation means that about 300 miles of transmission lines will cross over what used to be designated national conservation area. But the deal also increased the size of the conservation area, which experts say has the greatest concentration of nesting eagles, falcons and hawks in North America, with 3.5 square miles of key habitat.

The conservation area has prime nesting habitat for the birds in a deep canyon formed by the Snake River. They hunt ground squirrels and other wildlife in the surrounding sage brush steppe plains.

Officials describe the 500-kilovolt transmission lines as a freeway for energy that can travel in both directions and exit along the way to feed customer demand.

"The additional transmission capacity is going to allow for increased accessibility to the most efficient energy sources," said Idaho Power spokeswoman Stephanie McCurdy.

Idaho Power has about 534,000 customers in southern Idaho and eastern Oregon. Rocky Mountain Power has about 1.8 million customers in Oregon, Washington, Northern California, Utah, Idaho and Wyoming.

The U.S. Bureau of Land Management, an agency within the Interior Department, had been working on Gateway West since 2008, trying to thread the transmission lines through a mixture of private, state and public lands that include key habitat for sage grouse, a chicken-sized ground dwelling bird that has been considered for federal protections under the Endangered Species Act.

Approving the routes "advances a common-sense solution between federal, state, and local representatives to best provide for Idaho's energy needs and promote the region's energy infrastructure moving forward," said U.S. Sen. Jim Risch, R-Idaho.

The land management bureau over the last decade conducted extensive environmental analysis of the project's impact that required public involvement before reaching Wednesday's conclusion.

The process ended with the Interior Department's assistant secretary for Land and Minerals Management, Joe Balash, signing a document authorizing the bureau to offer rights of way for the transmission lines to Idaho Power and Rocky Mountain Power.

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