As Palo Alto continues to debate a contentious proposal to close Churchill Avenue to traffic near the railroad tracks, critics are posing a big question: Where will the 9,800 cars that use the street daily to cross the tracks go?

A new study by the city's consulting firm, Hexagon, offers some answers, even as it provokes more questions. The study, which the Expanded Community Advisory Panel discussed Wednesday afternoon, concluded that if the city kept Churchill open, traffic conditions would get significantly worse as Caltrain raises the number of hourly trains from nine to 12, consistent with the agency's business plan.

Closing Churchill, meanwhile, would worsen congestion at six intersections, though these impacts could be lessened through an assortment of traffic improvements on Alma Street and around the two most logical travel alternatives, Embarcadero Road and Oregon Expressway.

The study comes at a time when the city is trying to winnow down its menu of options for grade separation — a realignment of grade crossings so that local roads would no longer intersect with the railroad tracks. The City Council's list of grade-separation alternatives currently includes seven possible changes, including the closure of Churchill — an alternative that has divided neighbors near the tracks.

The option of closing Churchill has proved fairly popular in north Old Palo Alto and along Mariposa Avenue in Southgate, where many see the idea as a more benign and less disruptive alternative to the other option on the table: a train viaduct. Other Southgate residents, particularly those further from the tracks, have called for Churchill to remain open. They've argued that closing the street would make it harder for them to exit the neighborhood and would direct traffic to other east-west connector streets, most notably Embarcadero Road and Oregon Expressway.

The study by Hexagon offers some ammunition for both sides. The analysis indicates that if the city does nothing, traffic would get significantly worse as the number of trains increases, in some cases creating car queues that would take 10 minutes to clear. Closing Churchill, meanwhile, would create "significant impacts" to six intersections, which includes four around Alma Street (at Lincoln Avenue, Embarcadero Road, Kingsley Avenue and the Oregon Expressway ramps), as well as El Camino Real and Embarcadero Road; and El Camino Real and Oregon Expressway.

Hexagon also found that on four of these intersections, the impact could be minimized through various road improvements, including major changes to the congested interchange of Alma and Embarcadero.

Gary Black, a consultant with Hexagon, told the committee that once Caltrain increases to 12 trains per hour, northbound cars looking to turn left from Alma to Churchill would have to wait four to five traffic light cycles, or about 10 minutes during peak commute times.

The proposed improvements at the intersection of El Camino Real and Embarcadero include adding another left-turn lane on westbound Embarcadero to supplement the one that exists today and creating a right-turn lane on westbound Embarcadero for cars looking to go north. These measures, as well as improved synchronization of traffic lights, would reduce the traffic impacts and keep vehicle flow at roughly the level that exists today.

Hexagon also recommends the installation of traffic signals at the juncture of Alma Street and Oregon Expressway. And at the busy intersection of El Camino and Oregon Expressway, the proposal calls for a westbound right-turn lane from Oregon to El Camino as well as optimized traffic timing.

By far the most ambitious proposal is the plan to reconfigure the awkward intersection of Alma and Embarcadero. Today, drivers on Alma that want to get on Embarcadero (which dips below Alma) have to rely on neighborhood streets, including Lincoln and Emerson, to make the connection. Hexagon proposed a reconfiguration that would allow cars to use Kingsley Avenue, just south of Lincoln, to turn left or right on Embarcadero, shortening the drive through the Professorville neighborhood.

"Right now, the only way to make the connection is Lincoln to Emerson," Black said. "We wanted to provide another way to go."

The Hexagon study indicated that the improvements would lessen the impact at the Alma intersections to a "less than significant level." Yet it also concluded that even with the proposed improvements, traffic congestion would get slightly worse at El Camino's intersections with Embarcadero and Page Mill Road.

That finding echoes the concerns of Professorville residents who have complained that closing Churchill would divert traffic to other neighborhoods, including their own.

"If you want to facilitate movement, you don't close a crossing that gives you 10,000 crossings a day, because you would dump those, we would guess, 5,000 north to Embarcadero and 5,000 south to Oregon," Rob Levitsky, who lives on Emerson Street, told the committee Wednesday. "No mitigation or traffic study shows that you can just swallow those cars. That's ridiculous."

Kerri Yarkin, a resident of Churchill, took the opposite stance and said the traffic problems in her neighborhood are already severe. The mitigations that Hexagon is proposing should have been done years ago, she said.

"We've got a terrible situation right now and if you don't close Churchill it will be even worse," Yarkin said.

The committee, which is charged with advising the council on the preferred grade-separation alternative, had its own questions about the plan to reconfigure Alma Street. Chairwoman Nadia Naik and committee member Keith Reckdahl both asked Hexagon to provide more information about traffic conditions on Kingsley under the proposed plan. Naik said she was concerned about the prospect of cars queuing up on the right lane of Alma to turn on Kingsley under the new configuration.

The City Council has a goal of picking its alternatives for grade separation this spring.