Santa Rosa plans to sell four of its relatively new hybrid buses after a federal review found the city had more buses than it needs.

Four gasoline-hybrid buses that cost the city about $1.2 million in 2009 will be sold to the City of Gardena south of Los Angeles for $600,000 to reduce the size of the city's fleet.

The sale, expected to be approved by the City Council Tuesday, follows a review by the Federal Transportation Authority that found the city had more spare buses than federal standards typically allow.

The city has 37 buses, but only needs 24 to serve its peak afternoon demand, said Anita Winkler, the city's deputy director of transit.

That means the city has 13 spare buses, or 54 percent more than what's needed to serve peak demand. Federal regulations generally allow a ratio of 20 percent, though there is some flexibility for smaller system's like Santa Rosa's, Winkler said.

Santa Rosa began the process of purchasing extra buses when the economy was chugging along, said Jason Parrish, administrative services officer with CityBus.

The city had plans to build a rapid transit system that included dedicated bus lanes. But the recession hit, the expected growth never materialized, and the system has struggled. Last year low-volume routes were cut and fares increased.

So after the federal review discovered the extra buses, the city agreed to reduce the size of its fleet.

Instead of unloading its aging diesel buses, several of which have over 500,000 miles on them, the city instead chose to ditch its four New Flyer gasoline-diesel hybrids, which have been plagued by maintenance problems, Winkler said.

Keeping the buses on the road has been hard because the company that made their heavy-duty hybrid drive system, ISE Corp., filed bankruptcy in 2010. The city's extended warranties became worthless and parts have been hard to come by.

The result has been that when those four buses have gone down, they're often out of circulation for three or four months, Parrish said.

"Basically, we're paying through the nose for our maintenance costs," Parrish said.

Clean air regulations also require the gas engines in the buses to be replaced every 110,000 miles, far earlier the their diesel counterparts, said Jon Merian, the city's fleet superintendent.

While Santa Rosa only has the four, Gardena has a fleet of hundreds of gas-hybrid buses, in part because stricter air regulations in Southern California have discouraged diesel usage, Parrish said.

Gardena plans to strip the four hybrids for parts and convert the bodies into to all-electric technology, Parrish said.

Santa Rosa may back away from hybrid technology altogether until prices improve. Straight diesel buses run $400,000 versus $650,000 for hybrids, and have lower maintenance costs, Parrish said.

Future purchases to replace the oldest buses in the fleet will likely be diesel buses instead of hybrids, Parrish said.