Opponents of the project have been attacked as mere Nimbys, but many of their objections have merit. They have questioned the track alignment, financing and ridership projections, and some complaints were borne out by a recent state auditor’s report that criticized H.S.R.A. operations. A 2003 study of transportation megaprojects around the world showed that ridership projections almost always turned out to be wildly overstated, while costs were wildly understated.

The cost projection for the California project has already risen to $42.6 billion from $34 billion just for the initial San Francisco to Anaheim line. Rod Diridon, a member of the H.S.R.A. board and a longtime champion of rail transit in San Jose, said the increase was a result of a change in methodology — using “construction year” costs as opposed to current dollars — and the new number should be reliable.

The new chief executive of the H.S.R.A., Roelof van Ark, has considerable experience in Europe running high-speed train contractors, and presumably knows what he’s doing from an engineering and financial standpoint.

But it’s the political side of things that will make or break the project. The state bond money requires matching funds, which will come mostly from the federal government, and the $1.85 billion in federal stimulus money promised so far has deadlines attached — and is of course only a downpayment on what the government and private sector partners will ultimately need to provide. If local opposition causes delays, or forces too many expensive compromises, the financial side of the project will crumble.

But, still, the H.S.R.A. should not steamroll opposition. Hundreds of public meetings have been held, and if anything, agency officials and their consultants need to engage more aggressively with all constituencies.

Engineers, by training and disposition, are oriented to technical solutions and are often not very good at community engagement. We can only hope that Mr. van Ark, an outsider and an engineer, is a quick study.

It’s also incumbent on political leaders at all levels to engage the real issues, deflect the bogus ones and push the project forward. The debacle of the new Bay Bridge span — over a decade late, and many billions over budget —is a salutary example of where political bungling and poor engineering management can get you on a project of this scale. Hopefully, high-speed rail will stand as an example of a megaproject done right.