PER-HAPS this white elephant will be built. But there is absolutely no guarantee. Will bankrupt California be in a position a decade from now to still be pouring money into this hole? Current estimate is $68 billion. Thus if the Boston Big Dig has taught us anything, assuming you were a complete moron and didn't know it already, $68 billion is a hopeless pipe dream that will be no better than 50% of the final cost ASSUMING everything goes letter perfect.
If it were to be completed my guess, which is FAR better than theirs but still only a guess, is for $225 billion with construction completed in 2042. 400% over budget on money and 100% over budget on time. That sounds historically accurate.
One has to wonder what sort of road they could build for $200 billion, or even $100 billion. I envision I5a I5b I5c I5d; each of them 12 lanes with automatic switching so each 50,000 cars would travel a different road. Couple this with I5e and I5f dedicated to self driving cars traveling at 150 MPH and the california bullet train looks like a bigger dinosaur than the F-35-never-to-fly-in-combat USAF boondoggle.
And all this leaves out the fact that in the next 50 years there will probably be some big earthquake that damages the line. Creating a huge infrastructure item with a single point of failure is just plain stupid. Say it all works. It won't. But say it does. Say they ignore primary transportation and funnel all the gas taxes into this thing to the point they have to close I5. Now when anything from earthquake to terrorists to sinkhole breaks it for 6 months, or maybe 18, what the hell are you going to do?