Atherton, Menlo Park and three environmental groups Thursday filed a petition in Sacramento County Superior Court asking a judge to reopen their lawsuit against the California High-Speed Rail Authority, a move they hope will force the state agency to re-examine running bullet trains through the East Bay rather than the Peninsula.

Calling the rail authority's revenue and ridership models "obviously and fatally flawed," the groups asked Judge Michael Kenny to vacate his 2009 judgment upholding the Peninsula route and order the agency to consider new evidence before certifying program-level environmental documents.

"The numbers for the whole system are completely unreliable," said Richard Tolmach, president of the California Rail Foundation, one of the petitioners in the case. "They really have to discard the entire Bay Area to Central Valley environmental study. ... Having chosen the program-level alternatives on a falsified basis, it contaminates the whole product."

The ridership challenge is a new legal salvo in a long-running battle over the high-speed rail line's route through the Bay Area. It could also represent another threat to the state rail authority's credibility, which took a hit last month with the release of a critical state auditor's report.

Authority staff responded Thursday by defending the ridership numbers as "sound" while pledging to review the allegations made in the filing. Rod Diridon, a member of the authority's

"The issue of re-establishing the Altamont corridor is not open for discussion," Diridon said, referring to the East Bay route.

The petition to reopen the suit relies on a new report Norm Marshall, of the Vermont transportation planning firm Smart Mobility Inc., prepared for the petitioners. He wrote that several key numerical assumptions used to calculate the rail authority's ridership projections changed drastically after a peer review panel gave its stamp of approval.

In his report, Marshall calls the assumptions invalid and notes that the changes were not disclosed to the public during the 2007 environmental review period.

The rail authority originally assumed the length of a train trip was about five times more important to a potential rider than how often the trains depart — a ratio Marshall called reasonable. However, the authority based its final ridership numbers on a vastly different assumption that suggested riders care equally about trip length and train frequency, the report said.

"This is contrary to common sense, and if true, would cancel out much of the rationale of high-speed train service," Marshall said in the report.

The changed formula skewed ridership projections in favor of Pacheco Pass and the Peninsula over Altamont Pass and the East Bay, according to the report. That route selection was the subject of the groups' original 2008 lawsuit against the rail authority.

Though he essentially supported the bulk of the authority's work, Judge Kenny last August did find that its environmental impact report failed to provide an adequate description of the project or include proper land-use analysis. He also said the authority should have recirculated the documents after Union Pacific Railroad Co. refused to share its tracks with bullet trains.

Skepticism predates bond

Questions over the authority's ridership estimates aren't new. Even before voters passed the $9.95 billion bond measure authorizing the project in November 2008, skeptics had called estimates of 55 million riders by 2030 outlandish.

Scrutiny intensified after Elizabeth Alexis, a Palo Alto rail watchdog with a background in econometrics, dug into the numbers last fall and began finding things that didn't add up. Alexis' work — first reported by The Daily News in February — spurred the groups suing the authority to hire their own consultant to investigate.

The Smart Mobility report appears to back up Alexis' claims, raising questions about constants inserted into the model without an obvious basis in data. Those "fudge factors," it says, were also left out of the public documentation.

Alexis said Thursday those constants would have raised immediate red flags if they had been disclosed.

But rail authority Board Member Diridon on Thursday said he has no concerns about the ridership model. He questioned the reliability of Smart Mobility's report, pointing out that the environmental groups involved in the lawsuit bankrolled the study, which hasn't gone through a public vetting process.

"We're very convinced that the ridership study was done properly," Diridon said. "It was done by a world-class, highly respected review organization.

"We weren't trying to prove a point," he added. "We were trying to gain facts. These folks were trying to prove a point, and they seem to have gone out and hired an organization that proves their point."

Moreover, the ridership issues were just one part of the decision to run the trains through Pacheco instead of Altamont, Diridon said. He noted that East Bay cities, such as Pleasanton and Livermore, made it clear early in the process that they didn't want high-speed rail.

"Nonetheless, the California High-Speed Rail Authority will look at the data, will give it every consideration, and will respond to it" as legally required, Diridon added.

Authority's response criticized

Alexis said Thursday she has been disappointed by the authority's response so far but expects the Smart Mobility report to gain further support with the upcoming release of a University of California, Berkeley ridership study. Yet she said the authority continues to base important decisions on the flawed model and has rehired the consulting firm Cambridge Systematics for further work.

"It's still upsetting that the authority is not more curious, is not leading an investigation into their own numbers," Alexis said. "When you see something like this, aren't you asking questions of your consultants, and shouldn't there be some consequences?"

Ridership modelers don't always see eye to eye, and Marshall, who has done work for environmental groups and government agencies, said he sometimes comes across errors that aren't of importance while performing reviews.

"This is an important one that's very hard to justify," Marshall said, referring to the coefficient change. "It wasn't disclosed, and it does bias the results."

The petition filed Thursday goes further, accusing rail authority consultants of changing "the modeling parameters to produce a revised model" when the peer-reviewed formula didn't produce the ridership projections they wanted.

"There's no evidence at this point as to whether this was innocent incompetence or intentional, and that's why we've asked for the appointment of a special prosecutor," Transportation Solutions Defense and Education Fund President and petitioner David Schonbrunn said Thursday. "By specifically jacking up the coefficient for frequency, it gives an innate advantage for Pacheco over Altamont."

In a statement released Thursday afternoon, rail authority Interim Executive Director Carrie Pourvahidi said her agency takes the allegations seriously and plans to review them.

"We continue to believe that the ridership model is sound, however, we will carefully review the many and complex claims made in today's filing," the statement said.

E-mail Jessica Bernstein-Wax at [email protected].