The state Transportation Commission has approved $34.8 million to replace a Highway 101 bridge near the Petaluma River.

The construction work should begin this fall, according to Suzanne Smith, executive director of the Sonoma County Transportation Commission.

The funds were approved on Wednesday and are the last of the money needed to replace the complex of four bridges of the freeway over the Petaluma River and Highway 116 in southern Petaluma.

The work is part of the freeway widening project in Sonoma County and the Novato Narrows, which when finished will have a total cost of about $950 million.

Two critical parts of the project, the Highway 101 overpass of Wilfred Avenue, $65.4 million, and widening of the freeway from Rohnert Park Expressway to Petaluma Boulevard North, $148.2 million, are also expected to open this fall.

However, Sonoma County still needs $177 million to complete the widening through Petaluma and from Petaluma to the Marin County line.