A $68.7 million contract has been awarded to an Oakland firm for the next major round of construction on the Sonoma-Marin Area Rail Transit system. Most of it will go for track work in Marin County, but some of it will also go to Sonoma County.

Shimmick Construction will build a new operations and maintenance facility at Airport Boulevard in Santa Rosa, the northernmost end of the first first phase of rail service. It also will build a new Petaluma River bridge, replacing the existing Haystack Bridge, plus bike paths in both counties and finishing work on station platforms.

The regional commuter rail system hopes to begin testing trains on the tracks next year and launch commercial service in 2016 between San Rafael and Santa Rosa.