Building the California high-speed rail system won't be a free ride. It will require spending money that could otherwise fund education and health care.

Perhaps the most misunderstood aspect of bond financing is that it's a loan. It must be paid back. When the state borrows, the repayment usually comes from the general fund. While the legislative analyst warns that balancing the state budget in coming years presents daunting fiscal challenges, high-speed rail advocates want us to take on more obligations.

Think about it: If you were struggling to cover your mortgage, pay bills and feed the family, would you borrow to buy a boat? Or, in this case, to jump-start construction of a highly speculative train system?

Fortunately, when voters in 2008 approved bonds for high-speed rail, they also provided the Legislature the authority to stop it. Any members who approve the borrowing must explain why they support funding a rail plan we now know will likely never be completed rather than our K-12 schools, colleges and universities, or desperately needed care for the poor and elderly. That's the trade-off.

California voters repeatedly are asked to approve borrowing for state projects without raising taxes. They're never asked what they want to give up. That means they don't confront the financial consequences of their decisions.

Special interests line up with campaigns to take advantage of this. In recent years, for example, they have convinced voters to approve borrowing for freeway upgrades, public transit, battered women's shelters, senior housing, school construction, flood control, park acquisition, coastal protection, stem-cell research facilities and high-speed rail.

In the past two decades, California bond borrowing has rapidly increased. The cost of annual payments ate up less than 2 percent of the state general fund until 1990. Today, it's 6 percent and forecast to rise to 7 percent next year. That's currently more than $5 billion annually from the state general fund. Payments on the high-speed rail bonds would eventually add as much as $750 million a year.

Yet the bonds would cover just a small fraction of the project. Voters approved borrowing $9 billion for high-speed rail. Total cost for a system stretching from Sacramento to San Diego was estimated at $45 billion. The rest of the money was to come from the federal government and private investment. But the project voters approved is not the one on the table today. The cost estimate increased to $98.5 billion to $118 billion for a system linking just San Francisco and Anaheim.

Only $3 billion of outside money, mostly from one-time federal stimulus funds, has been secured. Beyond that, backers desperately argue that private investors and the federal government will eventually come through if taxpayers pony up first.

It's not only fantasy, it's insulting -- reminiscent of mortgage brokers at the peak of the housing bubble who issued loans promising unrealistic future dividends without regard to the consequences to the borrowers.

Make no mistake: The state should float bonds to borrow for needed capital projects -- provided it can pay back the money and the projects provide commensurate long-term assets. But the state can't pay its current obligations, much less add more. As for high-speed rail, the chances this project will be completed are slim to none.

To be sure, the state general fund problem stems in part from lack of revenue. California should collect more tax revenue. But lawmakers can't agree on how, and most voters, even though they want bond-funded projects, don't want to pay more taxes. Moreover, even if there were more revenues, highly speculative high-speed rail still would fall way down the list of spending priorities. Trains would be nice, but we can't pay for essentials.

The 2008 ballot measure provided a safety valve: The rail bonds require legislators' approval. They should reject them for two reasons. First, the current plan is not what voters approved. Second, we can't afford it.

Daniel Borenstein is a staff columnist and editorial writer. Contact him at 925-943-8248 or dborenstein@bayareanewsgroup.com. Follow him at Twitter.com/borensteindan.