A proposed corridor for high-speed trains through the Pacheco Pass between Gilroy and Chowchilla has received yet another vote of approval from the California High-Speed Rail Authority.

Meeting Thursday in Sacramento, the authority's board adopted an environmental impact report for a 175-mile stretch from San Francisco to the central San Joaquin Valley. The document is called a "program-level" report that reviews potential effects of the train system in broad corridors.

A more detailed analysis is expected to follow in a "project-level" report that narrows down to specific routes in the corridor.

This is the third time that the agency has approved a "final" program EIR for the Bay-to-Valley portion of the project.

Two prior votes -- one in 2008, another in 2010 -- were challenged with lawsuits, resulting in judgments invalidating the earlier approvals and court orders for changes to the documents.

An Oakland attorney representing the Bay Area town of Atherton in those suits told the authority's board that the latest version still leaves much to be desired.

"We appreciate some of the changes the authority has made in the past year," said Stuart Flashman. "But we do not think this EIR is ready for prime time."

"You may be thinking of the phrase, 'The third time is a charm.' But there's another phrase about three strikes," Flashman added.

Atherton and some other cities along the San Francisco Peninsula fear that although the rail authority is planning to improve and share tracks now used by the Caltrain commuter system between San Jose and San Francisco -- a "blended system" identified in the authority's latest business plan -- the environmental report includes an analysis of elevated tracks that would be used only by high-speed trains in addition to shared-track plan.

Opponents of the Pacheco Pass option say they prefer that the authority adopt a route that takes the tracks through the Altamont Pass between San Francisco Bay and Stockton. Both the Altamont and Pacheco corridors would affect some wetland habitats as they run from the Bay Area to the Valley. But the authority's planners said those habitat effects would be somewhat less in the Pacheco Pass.

Kathryn Phillips, representing the Sierra Club of California, told authority members that "it would be our preference not to put it through any wetland."

Before voting, board members said they faced a difficult choice.

"The Altamont alternative has a lot to commend it," board member Jim Hartnett said. But, he added, "in my heart of hearts, I still think Pacheco is the preferable alternative."

On the heels of that vote, the authority Friday is expected to release another environmental report, this one firmly establishing the proposed route for high-speed trains between Merced and Fresno -- a section that would be among the first portions to be built and operating with high-speed trains over the next decade.

A draft version was published last summer for two months of public comment. The document -- several thousand pages of information -- outlined the anticipated effects of 220-mph trains on cities, homes, businesses, farmland and the environment.

The final version is expected to include substantial changes reflecting the authority's responses to comments and criticism from property owners, elected officials, environmentalists, farmers and government agencies.

The report is required under both federal and state environmental law before the state rail authority and the Federal Railroad Administration can proceed with actual construction of the project.