Caltrans opened a new interchange at Airport Boulevard and Highway 101 on Thursday evening providing traffic relief for thousands of commuters and airport passengers.

The $51 million project, the last piece of nearly continuous highway construction along the 101 corridor from Cotati to Windsor since 2006, is part of the remaking of the transportation landscape at the business hub between Santa Rosa and Windsor.

“We’re really excited to be able to open the interchange at Airport Boulevard,” said Suzanne Smith, executive director of the Sonoma County Transportation Authority. “Since it will open up the access point to the Airport Business Center, it was important to help get traffic through there quickly.”

The project, which took a year and a half to complete, includes a wider Airport Boulevard overpass, new on- and off-ramps and sound walls through Windsor. It was built with $20 million in local Measure M sales tax money, which transportation officials were able to use as leverage to attract more than $30 million in state and federal funds.

“The Highway 101 project has been extremely successful particularly when it comes to leveraging state and federal money,” said Supervisor Mike McGuire, and SCTA board member. “The Airport interchange is a connector to Sonoma County’s future economy.”

Two years after Caltrans widened the highway to six lanes through southern Santa Rosa, Sonoma County voters passed the quarter-cent Measure M sales tax in 2004 to help expedite long-overdue improvements designed to alleviate traffic on Highway 101. That work began in 2006 with highway widening and interchange upgrades, first through downtown Santa Rosa, then north to Windsor and south to the northern edge of Petaluma.

As projects in central Sonoma County wrapped up and focus shifted to widening the highway through the Sonoma-Marin Narrows south of Petaluma — a project that remains under-funded — officials were able to secure funding to complete the Airport Boulevard interchange.

“It was all about leveraging funds,” said Sam Salmon, a Windsor councilman and SCTA board member. “It was a task that was well executed. We all voted for Measure M, and this shows that the money was well spent.”

The upgraded interchange will serve the 6,000 workers at the Airport Business Center as well as the 18,000 monthly passengers that use the Charles M. Schulz-Sonoma County Airport. Construction on the interchange caused bottlenecks and long delays for motorists, who faced lengthy detours on Fulton and Shiloh roads.

With the opening of the new Airport Boulevard ramps, Caltrans permanently closed the Fulton Road interchange since it was less than a mile from the new one.

Other ongoing transportation projects in the area include a commuter rail station and a lengthened airport runway that could help attract more commercial air service. Future plans call for widening Airport Boulevard west of the freeway, a park-and-ride lot at the interchange and a landscaping project.

Final work to touch-up the pavement at the new interchange will continue into next week, Caltrans spokesman Allyn Amsk said. A ceremony to formally christen the project is scheduled for Monday.