There is visible progress being made on the Highway 101 improvement project between Petaluma and Novato, affectionately known as the Sonoma-Marin Narrows.

To recap, ongoing work between Lakeville Highway in Petaluma and Atherton Avenue in Novato, a 9.5-mile stretch, will add frontage roads, widen bridges and improve three interchanges. Construction will continue into 2017, at which time the stretch of freeway will be safer and more modern, but it will still be four lanes. A separate project to add carpool lanes through The Narrows remains $250 million short.

As projects in The Narrows are completed, they will open, meaning motorists will notice incremental changes to the landscape rather than a grand opening of all the facilities at the end of the project. A few such pieces are already open.

At the southern end of The Narrows, crews are extending the northbound carpool lane by 1.4 miles from Atherton Avenue to near the Redwood Landfill interchange. That project, which includes a widened overpass bridge, is scheduled to open in the Fall, according to the Transportation Authority of Marin.

A new frontage road west of the freeway opened on July 18. That road leads from Atherton Avenue to Olompali State Park, and is now the only way to access the park. The park turnout directly off of Highway 101 closed when the new frontage road opened.

Just to the north, the Redwood Landfill interchange project, which will widen the overpass and add new on- and off-ramps, will see traffic shifts this weekend. The northbound on and off-ramps will be closed from Friday evening through Monday morning so that crews can build new ramps, which will open at the end of the weekend. The entire project, including a frontage road on the west of the freeway linking with San Antonio Road, will open this Fall, according to TAM.

North of the county line, workers are busy completing the South Petaluma Boulevard interchange. A new overpass and southbound on- and off-ramps are now open, and progress is being made on the northbound ramps.

The biggest project in The Narrows, widening the Petaluma River Bridge, remains on track to open in 2016. Crews are working on widening the middle section of the bridge, and the new bridge deck should be completed in August, according to the Sonoma County Transportation Authority.

The last piece of the ongoing work, the interchange at Lakeville Highway in Petaluma, should open next year. Workers are currently building the northbound bridge over Highway 116. Highway 116 will see nighttime closures tonight through Friday night as workers install a temporary structure that supports bridge construction.