Bay Area transportation leaders on Wednesday approved the region's deal with the state to split the $1.5 billion cost to electrify the Caltrain line that would ultimately be shared with statewide bullet trains.

"It will be much-improved train service in the corridor and it allows us to get some relatively early benefits of the spending of the high-speed rail funds without having to wait 10 to 20 years," San Jose Mayor Chuck Reed, whose administration helped draft the deal, said in an interview after the vote.

However, lingering questions remain over whether the new plan to run both Caltrain and state high-speed trains on an electric version of the existing two-track system is legal because voters in 2008 approved a high-speed rail line that assumed four tracks.

By sharing a pair of tracks with Caltrain, it could take California high-speed trains 45 minutes to travel between San Francisco and San Jose on their way to Los Angeles, instead of 30 minutes with four tracks. The slowdown also calls into question whether the state can meet its legal mandate to whisk bullet trains between San Francisco and Los Angeles in 2 hours, 40 minutes -- a requirement that relied on lightning-quick speeds in the Bay Area.

Engineers also were banking on up to 10 high-speed trains per hour in each direction with an expanded railroad. But with fewer tracks, officials say, six Caltrains would run each hour, leaving room for just two to four high-speed trains in the Bay Area. With slower trip times and a reduction in service, the rail line's ability to attract riders could be hindered, leading to a possible violation of the law that requires the rail line to break even and avoid a tax subsidy.

Lastly, the measure voters approved requires the new system to reach the new Transbay Terminal in downtown San Francisco, and critics have questioned whether sharing the existing Caltrain corridor is enough to meet that criteria.

The California High-Speed Rail Authority refused to say whether the railroad will ultimately be expanded to four tracks, saying specifics will be unveiled in a final business plan due next week, though its attorneys maintain using two tracks would be legal. Peninsula officials aren't buying the two-track plan as permanent, however.

"They're playing a very devious game here, telling people who want to hear that it's going to meet the time requirements that it's going to be a four-track system, and telling people on the Peninsula it's going to be a two-track system," said attorney Stuart Flashman, who represents Peninsula cities that have sued over the bullet train project. "And obviously it can't be both."

Still, officials around the Bay Area touted the smaller, two-track project as a compromise meant to lower the total cost of the $100 billion high-speed railroad and diminish the damages to Peninsula communities along the corridor. For cash-strapped Caltrain, it means lower operating costs and more frequent service.

Wednesday's "action represents the first step in what will eventually be a great leap forward for transit on the Peninsula," Caltrain CEO Mike Scanlon said in a statement.

The unanimous vote by the Metropolitan Transportation Commission represents one half of the political deal released last week. The Bay Area will contribute $750 million, mostly from federal grants earmarked for transit construction and tax revenue from San Francisco, San Mateo and Santa Clara counties.

On April 5, the rail authority board is set to approve its half of the deal to kick in $706 million in state bond funds, subject to approval by a divided Legislature as early as this June. Electric Caltrain service could open some six years after lawmakers approve the funds, with state bullet trains coming a decade or so later if funds can be secured to extend the tracks to San Jose from the starting point in the Central Valley.

Contact Mike Rosenberg at 408-920-5705.