After nearly a decade of dreaming, debating and designing, Palo Alto's bid to build a train tunnel from the north end of the city to the south came to a screeching halt Monday night.

In an unexpected move, the City Council voted 4-1 to eliminate from consideration what has been the most popular, the most expensive, and — in the opinion of most council members — most unrealistic alternative for separating the rail tracks from surface streets: A tunnel that would start near Channing Avenue and stretch south toward San Antonio Road.

The option, which has an estimated price tag of between $2.5 billion and $3.8 billion, is one of six that the council has been considering as part of its plan for "grade separation," the redesign of four rail crossings so that tracks and streets will no longer intersect. (The option to build a shorter tunnel, from Oregon Expressway south to the Mountain View border, remains in play.)

The council's decision came just three weeks after a divided council debated the idea of further studying the tunnel and ultimately failed to reach the four votes needed for a decision. The April 22 stalemate meant that the tunnel would remain in play, despite recent studies indicating that the option would require property seizures and would cost far more than any other alternative on the table.

Much like at the April meeting, Councilman Greg Tanaka lobbied hard on Monday in favor of keeping the tunnel in play and called the option a "multigeneration decision" that will have an impact for more than 100 years. He also accused staff and consultants of "bias" in their depiction of the tunnel's costs and impacts and challenged the engineering studies that suggested that the tunnel would require about 100 feet of space.

But unlike at the April meeting, when Councilwoman Lydia Kou joined Tanaka in ensuring that the short-handed council won't have the four votes it needs to eliminate the option (Mayor Eric Filseth and Councilwoman Liz Kniss were both recused because they own property near the tracks), on Monday Kou sided with the other three council members: Alison Cormack, Tom DuBois and Vice Mayor Adrian Fine. All three had argued at the prior meeting — and again on Monday — that the tunnel idea, while appealing to many citizens, is simply unrealistic.

Cormack said Monday that she supports eliminating the citywide tunnel because of its high cost and its impact on neighboring properties. An analysis by Aecom, the city's consultant, indicated that the city would need to acquire dozens of residential properties just east of the rail corridor to construct "shoofly tracks" — a temporary corridor that Caltrain would use while tunnels were being constructed.

Several residents told the council that it's time to pull the plug on the option, which became popular about a decade ago, when the city began bracing for the prospect of high-speed rail, a state project that has since been dogged by insufficient parking and flagging political support. Even with high-speed rail in limbo, the council remains focused on achieving grade separation to address the projected increase in Caltrain service.

"For a city of 67,000, to acquire $2 billion to $4 billion in debt would be an act of epic irresponsibility," resident Carolyn Schmarzo said.

She noted that if the city were to launch a GoFundMe site for the project, every resident would have to chip in $58,000.

Rob Levitsky, who lives in Professorville, similarly urged the council to nix the option. The city, he said, has neither the expertise or the funding to implement a tunnel. The project, he noted, is riddled with engineering challenges, including the need to get Caltrain's permission to construct the tunnel at 2% grade (which would require an exemption from Caltrain's standard of 1% grade) and the need for the new tunnel to cross Matadero and Adobe creeks.

"Accordingly, I believe it's time to say goodbye to the tunnel and remove it as an option," Levitsky said.

Not everyone was convinced that it's time to bury the idea. Stephen Rosenblum, who lives close to the California Avenue Caltrain station, echoed Tanaka's charge that the analysis presented to the council was "biased" against the tunnel, which staff had previously deemed financially infeasible. Resident Davina Brown also urged the council not to eliminate the tunnel option.

"I commend you for keeping all the options on the table and I sincerely hope you consider the future of Palo Alto, not just the costs today," Brown said.

Kou questioned Aecom's cost projections and pointed to the Central Subway tunnel project in San Francisco, which has a price tag of $1.6 billion (Fine countered that this project, unlike Palo Alto's grade separation bid, is a new subway project and, as such, does not require the disruptive and expensive construction of shoofly tracks).

Tanaka, for his part, challenged nearly every assumption that Aecom's engineers had made in their analysis, including the width of each of the two tunnels bores and the space that would be required between them.

The analysis indicated that the trench that would need to be constructed to accommodate the tunnel boring machine would need to be about 100 feet wide and 44 feet deep. This, according to the consultants, would be needed to accommodate the two bores (each of which would be 34 feet in diameter) and to have the needed space between the bores and outside the bores.

Tanaka argued that the tunnel's impacts can be significantly reduced if the option takes up less space. He disputed the engineers' idea that it would require 100 feet and said he's seen pictures of tunnels in which the bores were separated by about 5 feet of space, far less than the 15 feet the engineers said would be required. City Manager Ed Shikada, himself an engineer, countered that the space is needed to "ensure you have stable positioning" and to keep the two tunnels from interacting and interfering with one another.

Tanaka did not buy any of the explanations, calling them "incredibly biased," and argued that the council needs more information and a vote by the broader public before it could make a decision on the tunnel.

"We know it's something the community wants and yet some of the basic facts that determine the costs of the projects are not known at this point," Tanaka said.

Kou also requested more information about the project, including a more detailed breakdown of the various costs that comprise the consultant's overall estimate. Ultimately, however, Kou sided with the majority, a shift that seemed to catch most of her colleagues by surprise. At the end of the long discussion, which was dominated by Tanaka, the council voted to merely rename the tunnel option. Long referred to as a "citywide tunnel," the council decided to refine the definition to specify that the tunnel would start near Channing Avenue (to avoid reconstructing the downtown Caltrain station and interfering with San Francisquito Creek) and end at the south end of the city.

The council unanimously supported that option, as well as the idea of making public the city's cost estimates and technical assumptions about the citywide tunnel. After that motion passed, seemingly ending the discussion, Councilman Tom DuBois made a separate motion to eliminate the ambitious tunnel option. Unlike last month, Kou joined DuBois, Cormack and Fine and effectively killed the tunnel by a 4-1 vote, with Tanaka dissenting.

Even with the vote, the council is still exploring the idea of constructing a shorter tunnel — one that would stretch from south of Oregon Expressway to the city's southernmost border. Other options on the table are: a viaduct at Churchill Avenue; the closure of Churchill to traffic; a viaduct at the two southernmost crossings, East Meadow Drive and Charleston Road; a trench at East Meadow and Charleston; and a "hybrid" option that combines raised tracks and lowered roads at these two crossings.

The council has a target of making a final decision on its preferred alternatives for grade separation by this fall.