The California bullet train project has cost state taxpayers an average $3.1 million a day over the last year — a construction spending rate higher than that for the Bay Bridge, Boston’s Big Dig or any U.S. transportation project in recent history

But still it’s not enough, planners say.

In order to hit its 2033 deadline and $77-billion budget, the California High Speed Rail Authority will have to increase daily spending by up to nine times over the next four years or risk putting the already-delayed system further behind.