They pointed to the gap between those projections and 2010 ridership in Amtrak's Northeast Corridor, the nation's busiest rail line.

Using that comparison, the congressmen wrote, "we see how ridiculous those numbers seem."

In 2010, 10.3 million people rode Amtrak between Boston and Washington, D.C. "That's 19 million fewer passengers than California's 'low' estimation," they wrote.

Rail officials suggested that it was deceptive for the congressmen to compare ridership today in the Northeast with projected ridership in California nearly 30 years from now. "That's like comparing my ability today to dunk a basketball to my ability in 1962, when I could definitely dunk a basketball," Rossi said. "There's no comparison there. ... In fact, they've even got the wrong numbers."

California's ridership estimates for 2040 were generated by computer models based on high-speed trains that can make the 500-mile trip between San Francisco and Los Angeles in 2 hours, 40 minutes.

Amtrak's current service on the Northeast Corridor is a combination of conventional trains that make the 456-mile trip between Boston and Washington, D.C., in about 8 hours, and higher-speed Acela Express trains that shorten the trip to 6 hours 40 minutes. Those services combined for the 10.3 million riders in 2010. By 2040, Amtrak projects ridership in the Northeast Corridor to grow to 23.4 million as the region's population increases.

Amtrak is planning to develop its own "next generation" high-speed rail line, similar to California's system, in the Northeast Corridor. Amtrak forecasts that the project would boost train ridership on the corridor to between 34 million and 43 million a year by 2040, compared to California's 2040 estimates of 29 million on the low end and 43 million on the high end.

The U.S. Department of Transportation has committed about $3.5 billion to California to build the first section of the high-speed rail system in the San Joaquin Valley from north of Madera to Bakersfield.

The state must match that with about $2.8 billion from Prop. 1A. Construction would begin within a year and be completed by the fall of 2017.

Once the initial construction section is completed from Merced to Bakersfield, additional stretches of track would be added -- either northwest to the Bay Area or south toward the Los Angeles Basin -- before high-speed trains would begin carrying passengers.

Even a partial network of trains running from the north end of the San Joaquin Valley to the Los Angeles Basin would need only to attract 2.2 million riders a year by 2022 to break even on operations and maintenance, rail authority members said.

Amtrak's current San Joaquin route, with trains running from either Oakland or Sacramento, through Stockton and the San Joaquin Valley to Bakersfield with connecting bus service to Los Angeles, set a record last year with more than 1 million trips for the first time in 37 years of service.

In the Southland, trains from Los Angeles' Metrolink service provide about 1.5 million trips a year between Los Angeles and Palmdale.

Between the Amtrak San Joaquin trains and the L.A.-Palmdale Metrolink trains, "that's about 2.5 million riders in those corridors today," Richard said.

"If we actually close that gap down there with high-speed trains," Richard said of the distance between Bakersfield and Palmdale, "we only need 2.2 million -- and that's 10 years from now, with better and faster service -- to break even."