Palo Alto's effort to build a six-level garage near California Avenue moved ahead Thursday morning, when the Architectural Review Board signed off on the project.

By a 4-1 vote, with Robert Gooyer dissenting, the board threw its support behind the parking facility at 350 Sherman Ave. The garage will be four stories high and have two underground levels. It will occupy an existing city-owned parking lot.

The board's approval came after three public hearings. At the prior review on Jan. 18, board members criticized the proposed design, particularly the wall that was proposed for an area behind the staircase along the Birch Street frontage. In response, the city's architect for the project, RossDrulisCusenbery, proposed a new feature for the wall: a mosaic of porcelain tiles that will refract sunlight and create an "optical experience."

Mallory Cusenbery, principal at the firm, told the board that the mosaic will include three different tile types -- glossy, honed and textured -- that will reflect light and interact with sunlight and shadows in distinct ways. Though the wall will still look like one distinct color from a distance, as one moves closer, "its richness starts to show itself."

"Different tiles will behave differently, depending on how light hits them," Cusenbery said.

The firm made a few other modifications, based on the board's feedback. It removed a ground-floor column and replaced it with a beam so as to make it possible for the city to construct in the future a second exit from the garage to Jacarana Lane (this exit will not be constructed as part of the project). The new design also relocates a transformer at the garage site to a new location, at the corner of Ash Street and Sherman Avenue.

The board took some issue with the new transformer location and recommended that the council consider yet another place for the equipment. If it cannot be moved underground, the architect should create screening around the equipment, the board agreed.

After that quibble, board members generally agreed that the project has improved since they last saw it.

"I'm happy with how it's come along," said Board Chair Wynne Furth, minutes before the vote.

The board's approval represents a major milestone for the $40-million garage project, which is one of the central components of the City Council's infrastructure plan, which also includes a downtown garage, two rebuilt fire stations, a bike bridge over U.S. Highway 101 and a new public-safety building, which would be constructed next to the California Avenue garage, immediately after the garage is built.

For California Avenue merchants, the project also comes with a sense of urgency. The commercial neighborhood continues to experience parking shortages during the lunch hours. Jack Morton, president of the California Avenue Business Association, told the board Thursday that the merchants are "very excited" about the provision of the second exit, which they believe will be necessary and the potential of Jacaranda Lane to become a "community thoroughfare."

Though the project is moving along slowly, Morton said, "the result is something the business community and neighbors are excited about."