A proposal by three lawmakers to blend high-speed rail and Caltrain on the Peninsula received a boost Friday when a panel of experts retained by the California High-Speed Rail Authority (HSRA) decided to lend its support to the idea.

The rail authority's "peer review group," which is chaired by Will Kempton, submitted a letter to state Sen. Joe Simitian, D-Palo Alto, and state Assemblyman Rich Gordon, D-Menlo Park, largely endorsing the plan the two legislators and U.S. Rep. Anna Eshoo unveiled in April. Under the Eshoo, Simitian and Gordon proposal, the Caltrain corridor would be electrified and modified to accommodate both Caltrain and high-speed rail.

The rail authority, which is charged with building the voter-approved rail line, has so far focused on the "full build" approach, which calls for separate tracks for the new rail system.

In its letter, the group notes that the rail authority's demand forecasts remain uncertain and that the "full build" approach is "an unnecessary bet that the upper ranges of the demand forecasts are highly likely whereas the 'blended' approach would postpone larger investments until demand has been demonstrated by the initial services on the line.'"

The shared-tracks approach, the committee said, could also help the rail authority manage the new system. The agency has been in existence for more than a decade, but has spent most of this time advocating -- rather than planning -- for a new system.

"HSRA has, as yet, no actual experience with construction cost and management," the letter states. "Adopting a blended approach with local agencies would permit a sharing of the planning and management burden in those areas where HSRA could move up the learning curve on the higher speed section in the Central Valley."

The three legislators unveiled the plan largely out of concern about the way the controversial project is being managed. Early design plans, which called for the possibility of elevated tracks stretching along the Caltrain corridor, have galvanized Midpeninsula communities and have prompted various city officials, including the entire Palo Alto City Council, to formally oppose the project they once supported. The legislators have also been increasingly concerned about the cash-strapped Caltrain service and believe the electrification of Caltrain (which currently uses diesel) could increase its ridership and revenues.

The rail authority has been skeptical about the "blended" proposal, with several members of the agency's board of directors saying they were worried about the prospect of Caltrain dipping into high-speed-rail funds. Rail Authority CEO Roelof van Ark has also said that the blended approach could make it difficult for the rail system to meet its mandated goal of getting from San Francisco to Los Angeles in about two and a half hours. Earlier this month, when Caltrain released a study finding the blended option to be feasible, van Ark said such a system could be possible in the "near term."

The new findings by the authority's peer review group, which reports to van Ark, lend further credence to the legislators' proposal. The panel determined that the "blended approach" could make the system more financially feasible. The project, whose cost was initially estimated at $43 billion, is now expected to cost more than $60 billion. The 2008 bond passed by California voters allocates about $9 billion to the project and the rail authority hopes that federal and state grants, along with private investment, would make up the balance.

The rail authority decided late last year to launch the rail system in the Central Valley.

"A 'blended' approach would be much less costly at the outset than the 'full build' approach, meeting one of the fundamental objectives of efficient investment management, which is to shift investment as far out in time as is consistent with project needs," the panel wrote. "Given the large capital needs of the project, money saved can obviously be used elsewhere."

The committee's findings were greeted with enthusiasm by Gordon and Simitian, both of whom have been critical of the rail authority's projections. Gordon said in a statement that he appreciates the peer-review group's feedback.

"Their statement, in conjunction with last week's capacity study released by Caltrain, shows a way forward for a system that is consistent with the current rail system and also begins to address the concerns of the communities that will support it," Gordon said. "There is much work to be done, but I am encouraged by these statements."

Simitian, who has been one of the Senate's leading skeptics of the rail authority's projections and business plans, called the commentary by the Peer Review Group "particularly compelling given the professional expertise and experience of the Peer Review Group membership." Simitian said in a statement there appeared to be a "growing consensus in support of a blended system" and cited recent statements from the peer review group, Caltrain and various Peninsula cities. He also said he wasn't surprised by the panel's findings.

"My colleagues and I have been making the case that high-speed rail 'done right' means a 'blended system' along the San Jose to San Francisco corridor -- a system that integrates High-Speed Rail with a 21st century Caltrain," Simitian said.