Third Street in Santa Rosa at the railroad tracks just south of Railroad Square will be closed for two days, authorities said.
The closure took effect Tuesday evening and will be in effect through Thursday, said Santa Rosa Police Sgt. Eric Goldschlag.
The street will be closed in both directions while the Sonoma-Marin Ara Rail Transit does track work, Goldschlag said.
SMART officials could not be reached and the SMART website carried no information about the closure Tuesday night.
SMART is overhauling the train crossings as it rebuilds the track between Guerneville Road in Santa Rosa and downtown San Rafael for commute trains.
Service is scheduled to begin in late 2015 or early 2016.
The work on the crossings is a $12 million project to qualify them as quiet zones, where approaching trains may be exempted from blowing their horns.