Every rail transit system in the nation has a tax that pays or subsidizes its basic annual operating costs — except Caltrain.

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Editorial: Keep Caltrain rail service on track. Vote yes on Measure RR The commuter line’s cars are jam packed at rush hours between San Jose and San Francisco, sometimes running at 125 percent of capacity — standing room only. But Caltrain is funded as a sort of stepchild, with voluntary contributions from the Santa Clara Valley Transportation Authority, San Mateo County Transit District and San Francisco.

This year, for the first time, a regional poll of likely voters by the Silicon Valley Leadership Group found 74 percent approval of ballot language proposing an eighth of a cent sales tax for Caltrain. This would generate some $100 million a year from the three counties, replacing the “contributions” that currently fund the line and including a revenue stream for ongoing maintenance and to further modernize the system.

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That is an amazing level of support. But before the region can seriously explore whether and when to put a tax on the ballot, the state Legislature has to set the ground rules.

So state Sen. Jerry Hill, D-San Mateo, has submitted SB 797. It sets out a scrupulously fair procedure and a high threshold for placing something on the ballot, including support from all the counties and transit agencies and a two-thirds vote by the Caltrain board.

Lawmakers should approve it quickly to that leaders in the three counties can quickly begin their explorations: 2018 could be a prime year for a measure, since electrification of Caltrain is now under way, and further improvements of the line could be planned with a reliable source of revenue.

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There are 1.6 million jobs in the Caltrain corridor, through the heart of Silicon Valley, which produces 20 percent of the state’s sales tax revenue and 13 percent of its Gross Domestic Product. But commuting here is a nightmare, and better transit is the only practical strategy to get cars off the road.

Caltrain’s potential to do more is not theoretical. It is already a workhorse of the transit network between San Francisco and San Jose. This is one reason regional leaders won the hard-fought battle for federal funding this spring to complement state and local dollars and electrify the line.

That work, already begun, will mean cleaner air all along the Peninsula, with no more diesel, and more and faster trains. Reliable revenue will allow Caltrain to complete its modernization plan that includes longer trains, lengthening station platforms and providing for level boarding, no steps, which significantly speeds up service.

Any tax for Caltrain will require two thirds approval of the cumulative turnout in Santa Clara, San Mateo and San Francisco counties. This will not come easily. But there will be no chance of it happening if the Legislature doesn’t do its job and pass Hill’s legislation.

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