Caltrans is set to open a 1.6-mile carpool lane Saturday morning on northbound Highway 101 in Novato, another incremental piece of the Sonoma-Marin Narrows highway widening project.

The new lane, from just north of Atherton Avenue to just south of Olompali State Park, will ease the commute for northbound drivers at a key bottleneck where four lanes of traffic have merged into two. The $14 million project includes a widened bridge over Rush Landing Road, where traffic will now merge into three lanes through the 1.6-mile stretch.

Other pieces of ongoing construction on Highway 101 in northern Marin County include a new interchange at Redwood Landfill and frontage roads and bike paths along the highway. Those projects are expected to open next month.

Construction on the Sonoma County side, including the widening of the Petaluma River Bridge, is expected to continue into 2016. A $250 million project to ultimately widen the entire 13-mile corridor to six lanes from Petaluma to Novato remains unfunded.