Legislation that makes it next to impossible for the California High-Speed Rail Authority to build a four-track rail system on the Peninsula was signed into law Friday by Gov. Jerry Brown.

Senate Bill 557, spearheaded by Sen. Jerry Hill, D-San Mateo, and coauthored by Assemblymen Rich Gordon, D-Menlo Park, and Kevin Mullin, D-South San Francisco, seeks to address one of the region's primary concerns about the increasingly unpopular rail project – the prospect of a four-track rail system getting built along the Caltrain corridor.

The four-track alignment, in which Caltrain would occupy the outer tracks and high-speed rail the inner tracks, was initially proposed by the California High-Speed Rail Authority but later shelved in favor of a "blended system" in which both train services share two tracks on the Peninsula.

The bill creates a steep hurdle for reversing this decision. Though it stops short of codifying the blended alignment into law, it gives nine Bay Area agencies veto power over revisiting the four-track approach. The agencies include the Caltrain board of directors, the Santa Clara Valley Transportation Authority and the Metropolitan Transportation Commission.

The blended system, which was first proposed by former state Sen. Joe Simitian, Gordon and U.S. Rep. Anna Eshoo, would include as a major component the electrification of Caltrain, a project the commuter service has been planning for over a decade. Sen. Hill's bill makes Caltrain electrification more likely by including language that prohibits the transference of funds from the Peninsula segment of the high-speed-rail project to other regions of the state.

The bill clarifies that $600 million in high-speed-rail funds will be used to electrify Caltrain by 2019, with local agencies providing the balance of the $1.1 billion project.

The rail authority is now preparing to construct the first segment of the $68 billion San Francisco-to-Los Angeles rail system in the Central Valley. In a statement, Hill said the new law "provides statutory assurance that high-speed-rail funding will be used to advance the modernization of the Caltrain system and deliver cleaner, quieter, faster, more frequent rail service to Peninsula residents and business."

"By signing this bill, the governor has made it clear that the state is in lock-step with local communities advocating that the high-speed rail project should be phased to prioritize upgrades to our existing rail system and eventually accommodate high-speed rail service in a way that avoids impacts on local communities," Hill said.