With the traffic and parking impacts of Palo Alto's building boom dominating public discussion, officials on Wednesday balked at launching a zone change that would enable a four-story office building to go up at the city's most congested intersection.

Instead, an ambivalent Planning and Transportation Commission agreed to wait for more staff analysis before it rules on whether to initiate a "planned community" zone at a parking lot on the corner of El Camino Real and Page Mill Road. In a 5-0 vote, with Eduardo Martinez and Greg Tanaka absent, the commission agreed to revisit the project in four to six weeks, when staff returns with an independent analysis of the project's proposed benefits.

In its discussion, the commission grappled with the question at the center of every planned-community zone change, a mechanism that allows developers to exceed zoning regulations in exchange for public benefits: How much should the city demand from the developer in the zoning quid pro quo?

The Wednesday discussion demonstrated the city's changing approach to answering this question. In the past, the process of negotiating public benefits was a largely ad hoc and highly subjective affair, with council members declaring what they want the developer to provide and the developer modifying the offer over a series of contentious meetings. Recent "planned community" projects included in their list of benefits items such as art sculptures, public plazas, Caltrain Go Passes and affordable-housing units.

Now, the rezoning process is looking less like an art and more like a science, filled with economic projections and third-party analyses. In a sign of the times, commissioners agreed Wednesday not to vote on the zoning initiation until they have more information about the value of the zone change to the developer and the value of the benefits to the city.

The project at 2755 El Camino Real would be the second "planned community" project in this immediate area to fall under the new "Show me the money!" approach. On Wednesday afternoon, the city released such an analysis for a planned-community proposal that would stand about a block away, at 395 Page Mill Road, and that would feature 311,000 square feet of office space.

Jay Paul, the developer behind 395 Page Mill, offered to build the city a new police headquarters in exchange for permission to build two dense office buildings. The city's consultant, Applied Development Economics, concluded that the Jay Paul proposal could cover the cost of the police building and still bring the developer a 17 percent profit over a 30-year period.

For 2755 El Camino, both the scale of the project and the offered benefits are far more modest. The four-story building would be 33,500 square feet and the benefits include the widening of Page Mill Road to create a right-turn lane onto El Camino Real; an upgrade to a pedestrian tunnel on El Camino; and installation of pedestrian light poles on California Avenue.

Other suggested benefits, including various landscaping improvements and an offer to buy Caltrain passes for building occupants were dismissed by the commission as "mitigations," or conditions that the developer would likely have to provide anyway to get approval.

"When I think of public benefit, I don't think of it as mitigation of the problems your project is creating," Commissioner Alex Panelli said. "When I look at the list (of offered benefits), some of them feel like they are intrinsic."

Public benefits, he said, should either be "something that enhances for the benefit of all or helps to solve problems that already exist."

Vice Chair Arthur Keller, reflecting the prevalent view, said the benefits should be "commensurate with the benefit to the developer of increased development." He disagreed the suggestion from his colleague, Michael Alcheck, who said the city should look at what other planned-community projects in the area had to provide in benefits to get their zone changes approved.

Times have changed, Keller said, pointing to the "considerable complaints in the community about public benefits not benefiting the public."

Chair Mark Michael also endorsed the scientific approach and said commission's process for determining public benefits should be "consistent and predictable."

"We should be objective and analytical and make decisions based on rules that apply to us," Michael said, before concluding that the commission doesn't yet have the information it needs to be objective and analytical.

Cara Silver, senior assistant city attorney, said the process of commissioning independent economic analyses before ruling on a zone change was introduced during the council's recent approval of the Stanford University Medical Center expansion, a $5-billion project that the city green-lighted in 2011 after several years of negotiations.

"When that project went through, there was an overall recognition that the economic analysis was very helpful to decision makers," Silver said. "I think the council has indicated that an economic analysis in connection with PC projects is a worthwhile task."

So far, the project hasn't seen the kind of fierce neighborhood resistance that have characterized other recent planned-community projects, including the housing development proposed by the Palo Alto Housing Corporation for an orchard site on Maybell Avenue and the office-and-theater complex that John Arrillaga hopes to build near the downtown Caltrain station.

Chris Donlay, who lives a block away from 2755 El Camino, was one of only three people to address the commission at Wednesday's public hearing. He raised concerns about the potential parking and traffic impacts of the development, which is being proposed by Ken Hayes and Jim Baer on behalf of the property owner, Pollock Financial Group.

"It's under-parked and it's over-occupied," Donlay said. "While we as a neighborhood feel that rezoning may be a good idea, we do not feel cramming such a huge project into this site is a good idea."