COTATI – Caltrans opened the second of two new high-occupancy vehicle lanes in Cotati this morning, the latest development in a series of projects transforming U.S. route 101 in the North Bay.

The newly opened northbound lane joins the southbound lane opened on Dec. 3, creating a seven-mile stretch of “carpool lanes” in both directions between Rohnert Park Expressway in the north and Old Redwood Highway Bridge in the south.

Engineers chose to open the lanes early to provide congestion relief, saving the temperature-sensitive final paving until after the winter. Final paving, striping and new guardrails are expected to be implemented next summer, when the lanes will be closed periodically during non-commute hours.

The new lanes cost $82 million, with $80 million coming from voter-approved Proposition 1B bonds and a quarter-cent transportation sales tax in Sonoma County, “Measure M.”

Acting Caltrans Director Malcolm Dogherty said in a release that the lanes will lead to decreased congestion and improved air quality.

Additional work in Sonoma County is expected to be completed in late 2012 or early 2013. When the $40 million “Wilfred Avenue Interchange Project” is complete, Caltrans District One Spokesman Bob Haus said that the work will create “a solid, unbroken HOV lane from Windsor to Old Redwood Highway.”

More high-occupancy lanes are in the works through the “Marin-Sonoma Narrows Project,” which will add carpool lanes and improve freeway access between Novato and Petaluma. Crews broke ground on the project in July, with work expected to last two years.