The California Transportation Commission on Wednesday approved nearly $85 million to widen Highway 101 through Petaluma, an allocation that completes the funding package for a $121 million project to add a third highway lane from the Petaluma River to Corona Road.

The funding comes from SB 1, the state gas tax increase.

“Now it’s official,” said Suzanne Smith, executive director of the Sonoma County Transportation Authority.

The money will be appropriated for the 2018-19 fiscal year and Sonoma County officials hope to finish construction on the Petaluma project by the end of 2021, completing a more than $1 billion effort to widen Highway 101 from the Marin County line to Windsor that began in 2001.

South of the county line, Marin officials plan to use new bridge toll money, if a ballot initiative passes in June, to widen Highway 101 to Novato.

The highway project, through the heart of Petaluma, will facilitate the city’s long planned Rainier crosstown connector.

Rainier Avenue would extend from the Deer Creek shopping center, under a newly raised freeway, and over the Petaluma River and SMART train tracks to end at Petaluma Boulevard.

State Sen. Mike McGuire, D-Healdsburg, said in a statement he was pleased with the CTC’s decision to approve the funding.

“For decades, Sonoma County residents have been stuck in traffic at the bottleneck of the Narrows, and this funding is critical to advancing a big fix to a daily mind-numbing commute,” he said. “We know there’s more work to get three lanes all the way and we’re committed to getting the job done. Thank you to the California Transportation Commission, the Sonoma County Transportation Authority and the Secretary of Transportation for touring the corridor and understanding the need of North Bay residents. We are truly grateful.”