Sonoma County transit planners are treading a familiar path when it comes to their desire to replace a historic steel truss bridge near Sonoma.

They've gone before the county's Landmarks Commission on four occasions to present their ideas for replacing Watmaugh Bridge or building an entirely new span. But each time the plans were not well-received.

Tom O'Kane, the county's deputy director of public works, said he's not expecting a different outcome on Tuesday when planners officially seek the commission's blessing to replace the span.

"No, I think they've pretty much made up their minds that they want to have a retrofit rather than a replacement," O'Kane said Monday.

The Watmaugh bridge was constructed in 1929 to span Sonoma Creek and connect what is today Arnold Drive with Highway 12 leading into Sonoma. The bridge is one of two steel truss bridges in Sonoma Valley and in 1981 was designated as a county historic landmark after preservationists saved it from being torn down.

County officials say the bridge is at risk of collapse during an earthquake or major flood because of erosion around the piers that support it. But preservationists contend that officials are inflating the risks and that the span can be brought to safety standards without having to replace it.

The Landmarks Commission has the authority to review changes to the bridge under a 1998 Board of Supervisors resolution that designated Watmaugh and 11 other bridges part of a countywide historic bridges district. The ultimate decision rests with county supervisors.

County planners have tinkered with the plans to try and alleviate the concerns expressed by commissioners and by people who live near the current span. That includes scrapping a plan to build an entirely new overpass near where the current bridge stands.

The county's current plans call for replacing the existing bridge with one that is 32 feet wide, which is 12 feet narrower than initially proposed. The current span is 22 feet wide.

The county also is offering to rehabilitate the trusses and put them back on the bridge once it is replaced.

Tuesday commission meeting is at 5 p.m. at the county's Permit and Resource Management Department on Ventura Avenue.