Castilleja School suffered a blow Monday to its plan for modernizing its Bryant Street campus when a skeptical Palo Alto City Council demanded major revisions to the school's application, including a redesign of its controversial garage.

While the council didn't take any formal action Monday during its third public hearing on the school's contentious plan, its direction means that the school will have to modify its application and return for a fresh round of public hearings in front of the city's Planning and Transportation Commission and Architectural Review Board. It effectively ensures that the project, which has been in the works for nearly five years, will not reach the finish line any time soon.

Much like the broader community, council members expressed a wide range of positions on the school's redevelopment plan, which involves replacing campus buildings, building a new underground garage, relocating the school's swimming pool to an underground location and gradually expanding student enrollment from the current level of 426 to 540. Some, including Mayor Tom DuBois and council members Lydia Kou and Greer Stone, were deeply critical of the proposal and suggested that they could not support the plan in its current form. Others, including Vice Mayor Pat Burt and council members Alison Cormack and Greg Tanaka were more willing to advance Castilleja's project, albeit with some modifications.

Despite the division, council members generally agreed that the key to Castilleja's success is traffic management. The modernization proposal already includes a "no net new trips" requirement and an aggressive transportation-management program that relies on shuttles, carpools and bike programs to shift students and faculty away from cars. If traffic counts show Castilleja failing to mitigate traffic, the school would face penalties and lose its ability to expand enrollment.

But while the planning commission imposed this requirement to make sure that the school would limit its impacts to the surrounding neighborhood, council members said Monday that they are skeptical about the city's ability to enforce the traffic measures. Council member Eric Filseth wondered whether it's even possible for Castilleja to add students while keeping traffic levels steady.

"We're running up against some laws of physics here," Filseth said. "It's hard to have a destination school in a residential neighborhood that continues to grow and doesn't run into traffic problems. That's kind of what we're grappling with."

The council's biggest accomplishment over the course of Monday's five-hour discussion was reaching a decision on the plan's most contentious element: an underground parking garage. Having failed to offer a clear direction on the garage at its prior two hearings, the council backed on Monday the only compromise that could muster majority support: a scaled-down version of the underground garage that would accommodate up to 50% of the school's required parking spots, or 57 cars.

Vice Mayor Pat Burt said allowing the underground garage but in a reduced form achieves the "right balance" and alleviates community concerns about the facility, which many residents had criticized for being incompatible with the single-family neighborhood.

For DuBois, Kou and Stone, even the smaller garage proved too much. DuBois and Kou both said they would prefer no garage at all, while Stone asserted that he would need more information about the smaller garage before he could support it.

While the council's vote offers Castilleja a tenuous path forward, it effectively dashed the school's hopes that the project will advance any time soon. Instead, the project will now be remanded to the Planning and Transportation Commission, which had already held six hearings on the Castilleja project, and the Architectural Review Board, which reviewed the project over the course of three hearings. Each panel had ultimately voted to recommend approval of the project.

Tanaka said requiring a smaller garage constitutes "a total reset of this whole project."

"It's not like we're changing a window. It's an entirely different project," he said.

The council's abrupt decision to require a smaller garage appeared to catch Castilleja by surprise. Mindie Romanowsky, Castilleja's attorney, said the new direction would require the school to offer more surface parking on its campus, potentially infringing into its playing field and green spaces.

"My concern here is, if only 50% of the parking spaces are allowed to be underground, I'm not sure where else we'd park," Romanowsky said, "That's the concern."

Despite its split over the parking facility, the council largely agreed that Castilleja would need to definitively prove that it could manage its traffic impacts before it could increase enrollment. To that end, council members approved a two-page motion crafted by Stone and Burt that calls for stronger penalties for noncompliance, a possible creation of a TDM Oversight Committee and an increase in the proportion of Castilleja students within bicycle distance from the campus.

In another blow to the school, council members also indicated that they favor lowering the number of special events Castilleja is allowed to hold on its campus. After the planning commission recommended a maximum of 74 events annually (and none on Sundays), Kou suggested that the commission and staff consider limiting the number of events to between 50 and 70.