California High Speed Rail Authority board members listened, but took no action, Thursday when they were told in person that ridership estimates they're using to plan the 400-mile rail system are unreliable.
The forecasts "are not reliable for the purposes you need them to be," University of California, Irvine, economist David Brownstone told the board. "What they did not do is tell you what would happen if their statistical projections are wrong."
Brownstone is part of a team of UC researchers who last week released a study showing that based on the ridership estimates used by the Rail Authority, it is impossible to know if the $43-billion system will succeed or fail.
On Thursday, Brownstone detailed for the board why the study came to that conclusion.
One problem, Brownstone said, with the estimates provided by the Rail Authority's subcontractor, Cambridge Systematics, is that no one knows what the margin for error is. Or if someone does know, that someone isn't telling.
Cambridge Systematics President Lance A. Neumann stood by his company's estimates, telling the board they were facing an "academic" versus "real world" disagreement.
One board member revealed her view of the issue from the dais.
"Being married to a professor for 40 years," joked board member Lynn Schenk of San Diego, who was chief of staff to former Gov. Gray Davis, "I tend to discount a lot of what academics say. We, as policy makers, have to deal in the real world."
However, if the ridership estimates turn out to be wrong there will be some very real-world consequences for a high-speed system that would run between San Francisco and San Diego and hit many stops in between.
Without predictions of strong ridership, the California High Speed Rail Commission will not be able to attract large investors to help underwrite the project, and the rail system won't reach its goal of being self-sufficient by 2035.
Brownstone noted Thursday that in the past transportation planners typically either didn't include a margin of error in reports on their ridership estimates or simply didn't do it.
But, he said, recent research has shown that without those "error bands" the planners have no idea how accurate their projections are.
Following the hearing, he said in an interview that error bands are similar to the margins of error typically included in such things as political polls. An acceptable margin of error in political polls is usually about 5 percentage points. The value of an estimate goes down as the margin of error increases.
If Cambridge computed margins of error for its statistics, Brownstone said, and the margins were small, "they would have said so. My guess is they didn't do it."
The High Speed Rail Authority has been embattled on several fronts, from a highly critical state audit that found lax oversight of its main contractor, Parsons Brinckerhoff, to concerns about whether it will financially succeed as a high-speed rail system.