In a desire to explore what it describes as an innovative planning concept that could lead the state and nation in a new approach to managing development, the Palo Alto planning staff has opened up a potential can of worms that we hope the city council will approach with extreme caution.

The idea is one of four different "future scenarios" the staff has put together for how Palo Alto might develop over the next 10 or more years. If approved by the council when it returns from its summer break on Monday, the four alternatives will be analyzed in an environmental impact report required for the pending revisions to the city's comprehensive plan.

The idea is that if future development can somehow be controlled so there are no new impacts from the development, then it won't be necessary to use rigid measures such as growth caps, density and height limits.

The staff gives examples of this "net-zero" concept: net-zero greenhouse gas emissions, net-zero new vehicle miles traveled or net-zero new potable water use. If impacts can be kept to "net zero," the staff reasons, development brings little or no downside.

"No specific growth management strategy would be needed," the report states, "on the theory that the 'net-zero' requirements would address the pace and impacts of development."

The policy might be applied citywide or to specific areas. The report suggests that in applying this approach while planning for the future of downtown Palo Alto the current cap on growth in square footage would be replaced with a restriction on new vehicle trips.

Along El Camino Real, the long-range plan might designate certain areas for exceeding the 50-foot height limit "where projects would be models of sustainability, with small units, car share and transit access rather than resident parking, net-zero energy, and net-zero greenhouse gas emissions."

Stanford Research Park could become a "cutting-edge proving ground for innovative concepts in energy generation, carbon sequestration, recycled water, urban farming, and drought-tolerant landscaping."

The lofty goals, which sound like they come straight out of a planning school textbook, ignore the immense practical obstacles to making the "net-zero" impact concept work. The staff points to no municipality where this approach has been successfully implemented, and we challenge them to do so at Monday's council meeting.

Locally, Stanford has experienced a version of this concept through its development permit negotiated with Santa Clara County. Under that agreement, Stanford must demonstrate through regular independent traffic analyses that new development on campus has not worsened traffic conditions (no net increase in trips.)

That requirement has led to large investments by the university in traffic-reduction measures, such as carpooling, expansion of the Marguerite bus service and public-transit subsidies, and has been enormously successful. In spite of the addition of hundreds of thousands of new square footage on campus, there has been no net increase in car trips. Stanford's ability to continue to build depends on it continuing to restrain growth in traffic.

But while Stanford has been a model for this approach, it also is drastically different from adopting a "net-zero" concept to a city made up of a myriad of property owners.

At Stanford, a single property owner is accountable and pays the price (by being allowed no further development) if it does not meet the required goals. And measuring car trips to and from the Stanford campus, with its few entry points, is a simple proposition.

Based on past performance, it is naïve to think that Palo Alto and its consultants could devise a system that could reliably collect and analyze data of the sort the staff envisions. And it is even more naïve to think the community would have enough confidence in such a system to endorse this as a major pillar in our future planning strategies.

It is important to note that the planning staff's "net-zero" concept is only intended as one alternative for study in the environmental impact analysis and that any policy that might flow from that analysis is a long way off.

But we have seen what can happen when development policies are riddled with available exceptions, exemptions, bonus credits and other ways to bend zoning rules. This proposal runs the risk of creating an alternative that is largely experimental and unproven, and where accountability will be difficult. The council must send a clear message that it doesn't want to go there.