With development anxieties running high in Palo Alto, the city's planning commissioners on Wednesday pondered three different visions for long-term growth that carried one common theme: preservation of residential neighborhoods.

Members of the Planning and Transportation Commission also showed some interest in a fourth alternative -- an experimental "net zero" growth strategy that would encourage development that would, for example, generate no additional greenhouse gases, result in no additional miles traveled by vehicles or consume no additional potable water.

This concept, like the more conventional others, is set to be fully analyzed in the Environmental Impact Report for the city's Comprehensive Plan, a broad land-use document that city officials have been updating since 2006, when the City Council first proposed a revision. After eight years in planning purgatory, the update is finally flickering to life, with dozens of residents attending recent public hearings to voice their opinions on the city's long-term future.

Wednesday's hearing brought more than 20 residents to a discussion of a topic that in recent years has typically drawn one or two attendees to City Hall. The hearing followed three separate workshops on the Comprehensive Plan this spring, the most recent of which took place on June 24 and attracted more than 70 participants, according to the city's planning staff.

Of the three main concepts on the table, the first (known officially as the "do nothing" option but dubbed by commission Vice Chair Arthur Keller the "business as usual" option) would leave all existing land-use designations and policies in place. There would be no new garages and little residential development, according a staff report from Senior Planner Elena Lee.

The second and third alternatives call for "slow non-residential growth." The second concept would create new policies to control non-residential developments and allow just enough housing to meet the state requirements set by the Association of Bay Area Governments.

The third concept would be more aggressive when it comes to residential growth, allowing residential buildings near transit hubs to be taller than currently allowed. This concept would also develop the site at 27 University Ave. at the edge of downtown Palo Alto into an expanded transit center with housing.

While most commissioners agreed that the city's low-density residential neighborhoods should be protected, they offered a range of opinions on broader questions relating to growth. The city's 50-foot height limit was one topic of dispute, with three commissioners making the case that it should be relaxed.

Commissioner Michael Alcheck said he often encounters residents who want to keep the 50-foot height limit and don't want to see greater building density. He said he likes to remind them that growth is coming and to ask them where they would prefer to see it. Some areas, like the foothills, are clearly unsuitable for growth, he said. With sprawl also undesirable, that leaves infill development as the best alternative for adding density, he said.

Chair Mark Michael also made a case for embracing "change." The city should "allow for the creation of resources that the future will view as historic," he said.

"It's not growth. It's change. If you think of it as change versus no change, to me no change is a recipe for entropy, disaster and decline – not something any of us would appreciate. If we have a yard, we plant flowers, grow trees – we promote change. I think change is good if properly managed."

Relaxing the 50-foot limit, he said, would allow for an additional story where appropriate, in areas like downtown and perhaps California Avenue and El Camino Real.

"I think the sacrosanct nature of the height limit is a mistake, personally, but if it's the law I will follow the law," Michael said.

Commissioner Eric Rosenblum proposed going a step further than the third concept, which would raise the height limit from 50 to 55 feet for residential projects near transit areas. The limit should be 60 feet, he said.

"If we're going to violate historic precedent, it should be a meaningful violation," Rosenblum said.

Rosenblum also recommended that all of the concepts, not just the third one, plan for the 27 University Ave. site, which is located next to the downtown transit center and which was recently the focus of a controversial proposal by developer and philanthropist John Arrillaga. He criticized the main alternatives as being largely no-growth or anti-growth.

"There needs to be a scenario where jobs are also created or at least explicitly addressed," Rosenblum said.

Others were more cautious on the issue of height limits. Commissioner Przemek Gardias said the city should first look at redeveloping open spaces like parking lots before it allows taller buildings.

"That could be an opportunity for downtown as well as California Avenue without raising any limits," Gardias said, referring to the parking lots.

Beth Bunnenberg, a member of the city's Historic Resources Board, addressed the commission and recommended sticking to the 50-foot height limit.

"Keep the buildings of human scale, both residential and nonresidential," Bunnenberg said.

Keller was more cautious than his colleagues on growth. The demand for housing in Palo Alto is high, he said, but satisfying this demand will come at a price.

"It's certainly true that if you build it, they will come," Keller said. "If we allow them to build it, they will. We cannot quench the demand from people to live in Palo Alto. If we did allow everyone to live in Palo Alto, our schools would be so overcrowded that their quality would be destroyed."

It is not the city's objective, Keller said, "to make things nice for 'redevelopers' so that they can maximize their profits."

"What we instead want to do is to zone for what we want," Keller said.

Commissioners Greg Tanaka and Carl King made a case for protecting single-family residential neighborhoods, in keeping with all of the concepts in the proposed Environmental Impact Report. But Michael suggested that there should be some flexibility in making changes to single-family-residential (R-1) zones, saying there are many "empty nesters" (he used himself as an example) who may want to move out of their large homes and into smaller apartments.

"Not touching the R-1 in our zoning living space is a mistake," Michael said.

The commission also heard from numerous residents in an unusually packed Council Conference Room. College Terrace resident Kevin Murray said the goal of the revised Comprehensive Plan should be to "preserve the quality of life" the city currently enjoys and to protect residents from what he referred to as the "second Gold Rush."

"Your only role should be how to manage existing development rather than looking at future development," Murray told the commission.

Seelam Reddy, a candidate this fall for City Council, made a case for bringing in more medical services for residents who may not be able to afford to go to Stanford Hospital for treatment. He also advocated for beautifying El Camino Real and working more closely with East Palo Alto in planning for the future to help "lift up that community."

"We are not living in an isolated world," Reddy said. "Any of our planning, we need to work with them. Same with Mountain View and same with Menlo Park. What they do impacts us and what we do impacts them."

Shani Kleinhaus, an environmental advocate with the Santa Clara Valley Audubon Society, said she was concerned about the "net zero" alternative and suggested that the city carry out its net-zero experiments at the neighborhood level, rather than throughout the city.

"This is the kind of an experiment on a citywide scale which would be really scary because it could be an outcome that we don't expect at all," Kleinhaus said.

The city hopes to complete its update of the Comprehensive Plan by the end of 2015. The council is scheduled to discuss the Environmental Impact Report for the update on Aug. 4.