If Palo Alto didn't want bullet trains racing through town, it should have spoken up earlier, California High Speed Rail Authority board member Rod Diridon told the City Council on Monday.

The decision to run the 125-mph trains up the Peninsula via the Caltrain corridor was made in 2008 after years of debate, and revisiting it now could cripple the $40 billion Los Angeles-to-San Francisco project.

Instead, the city should focus on how to make the train work now that it has been approved by the state's voters, Diridon said. The rail authority has heard the city's desire to study running the line underground, and it will examine that possibility, he added. No decisions about the specifics of the tracks' design will be made until after an environmental review.

After unanimously endorsing the high-speed rail plan last fall, Palo Alto officials are struggling with its potential impacts. One possible alignment would put the tracks on a 20-foot-high concrete platform so the trains wouldn't intersect with cross streets. Residents, inflamed by the prospect of a "Berlin Wall" dividing their neighborhoods, have been packing public meetings on the topic.

On Monday, more than 50 people marched on City Hall ahead of the council meeting, carrying signs with slogans such as "Too close to my school," "Do it right," and even "Revote on Prop 1A." Voicing an increasingly popular sentiment, they chanted, "High-speed rail underground, we don't want to hear a sound."

The council responded by unanimously approving a formal letter to the rail authority calling for it to study the possibility of building a rail tunnel under the city. Despite Diridon's comments, the letter will also call for the rail authority to reopen the possibility of running the trains through the East Bay or along the Highway 101 or Interstate 280 corridors rather than along the Caltrain tracks.