Palo Alto has few great options for pursuing its most urgent and frustrating infrastructure priority -- a new police headquarters -- but three possibilities have recently emerged as the least bad of the bunch.

All three sites for the new building would require tradeoffs and entail debates about priorities. Yet they have one big edge over prior contenders: Each parcel is already owned by the city.

The new emphasis on city-owned land is a departure from past conversations, when it was generally assumed that the city would have to buy property to accommodate the new police headquarters. Though the city has been talking about the need to upgrade its small and seismically shaky police headquarters since 1997, all efforts to further this cause have so far ended in frustration. In 2007, the leading candidate was a property at 2747 and 2785 Park Blvd. The city bought a purchase option from the property owner, Essex Park Boulevard, LLC, but then terminated the agreement in June 2009 because of the economic downturn.

More recently, the developer Jay Paul Company offered to build a new police headquarters as a "public benefit" in exchange for the city's permission to build a massive office development at 395 Page Mill Road. That plan fizzled in December 2013, when Jay Paul withdrew its application, citing an unfavorable political climate.

Jay Paul had also purchased in January 2013 two Park Boulevard properties that the city had previously considered. After paying $11.4 million for the sites, the developer now plans to build a three-story office building there.

A new home for public safety has been one of the city's most pressing infrastructure needs for more than a decade. Several citizen committees, one devoted specifically to the public-safety facility and another that surveyed all of the city's infrastructure needs, emphatically concluded that the current facility is inadequate and that a new one is needed. At 25,000 square feet, the police headquarters at City Hall is about half the size the department says it needs; and a 2011 assessment by a citizens committee described the 1970 facility as "unsafe and vulnerable."

Last year, the City Council designated a new public-safety building as a top priority in the city's new infrastructure plan and identified $57 million that would be spent on it. Whereas five years ago, the city had a site but no money secured, today the reverse is true.

Over the past year, city staff considered more than 20 different sites, including ones located by the foothills at Deer Creek Road, at Palo Alto Square on El Camino Real and the animal shelter location on East Bayshore Road. These and many others were ultimately eliminated because they were either too small, too expensive, filled with too many uncertainties or simply not for sale. Three, however, made it to the final round and are set to be discussed by the City Council at a special meeting on May 6.

One option would place the police headquarters by the Baylands, at the former Los Altos Treatment Plant site at 1237 San Antonio Road. Another would place the headquarters at 3120 West Bayshore Road, the current location of a PG&E substation that would have to be relocated. Like the Los Altos Treatment Plant site, it is close to the Baylands but distant from the city's main commercial district -- a drawback but not necessarily a deal-breaker at a time when each police cruiser effectively acts like an office.

A third site, at 250 Sherman Ave., has a more central location: a 1.5-acre city-owned parking lot, known as Lot C-6, in the California Avenue business district. It's smaller than the other sites, however, and the city's evaluation notes that "program compromises may be necessary to fit PSB (the public-safety building) on this site."

Then there's the challenge of taking over a parking lot in an area where there's already a dearth of parking and that is currently going through a building boom. To address this problem, city staff is proposing an ambitious solution: building a new parking garage an adjacent lot, which is also owned by the city.

While the City Council has already committed to constructing a new downtown garage, which is a central part of its infrastructure plan, a new parking structure in the California Avenue area hasn't been firmed up. But there could be an incentive: Because building a police headquarters on Sherman would save the city the roughly $10 million it was planning to spend on acquiring a site, staff is now floating the possibility of using this money to speed up the timeline for a California Avenue garage.

A new report from the Public Works Department notes that the new garage "might also include ground-floor retail that could be designated as below-market-rate for preservation of locally owned shops."

The public-safety building, meanwhile, would have about 44,848-square feet of space, much more than the current facility but less than the 50,000-square-foot building considered previously. In addition to serving the needs of the Police Department, the building would have space for the Emergency Operations Center, the Office of Emergency Services and the administration of the Fire Department.

"The new PSB is expected to provide for the city's public safety needs over the next 50 years, as well as address and resolve compliance issues with seismic, accessibility, code and regulatory requirements," the Public Works report states.