The pace of work to widen Highway 101 through Sonoma County is picking up and shifting to Petaluma, where four major projects to rebuild overpasses and bridges will start within the next few months.

It will also probably make Petaluma traffic a mess until work is completed in late 2014.

"Patience will be required and tested with all the work being done," said David Rabbitt, chairman of the Sonoma County Board of Supervisors and a longtime Petaluma resident. "The widening project as a whole has been widely supported over the years. Once people see it finished, it will be very, very welcome."

Ghilotti Construction of Santa Rosa is expected to begin work to rebuild the Highway 101 interchange at Old Redwood Highway-Petaluma Boulevard North this spring after submitting the low bid of $19.6 million.

At the same time, work is also supposed to get under way on rebuilding the Highway 101 bridges over Highway 116 and the Petaluma River, the South Petaluma Boulevard overpass and some Highway 101 frontage roads south of Petaluma, at a cost of $119.7 million.

"We had all the work between Windsor and Petaluma the last eight years, and we are now going to see that shift to a lot of work happening from Petaluma to Novato over the next number of years," said Suzanne Smith, executive director of the Sonoma County Transportation Authority.

Work to widen Highway 101 to six lanes through Sonoma County began a decade ago, when a five-mile stretch of freeway was opened between Highway 12 in Santa Rosa and Wilfred Avenue in Rohnert Park.

Since then, an additional lane has been added from Windsor to the northern part of Petaluma, major overpasses have been replaced and soundwalls built.

The seed money for the work has been Measure M, a quarter-cent sales tax passed by voters in 2004. It has raised $140 million for Highway 101 construction and used as leverage to get $615 million more in state and federal highway funds.

When all work is completed, at a date that is still not determined, there will be six lanes of freeway all the way from Windsor and through the Novato Narrows to the Marin County line, at a cost of almost $1 billion.

"It will be great to have a modern freeway, border to border," Rabbitt said.

The interchange at Old Redwood Highway and Petaluma Boulevard North came in $2.3 million under the engineer's estimates, which is money that may be able to be spent elsewhere in the corridor, Smith said.

Ghilotti Construction is expected to begin work this spring and finish by late 2014.

Other work that will also get under way this spring in the Petaluma area is rebuilding a complex of four Highway 101 bridges that span Highway 116 and the Petaluma River, scheduled to cost $30.5 million.

An additional $89.2 million will be spent rebuilding the interchange at South Petaluma Boulevard and on frontage roads that stretch from Petaluma to the Marin County line.

Those projects are being built by Ghilotti Brothers of San Rafael.

In Windsor, Ghilotti Construction will begin work this spring to replace the interchange at Airport Boulevard, at a cost of $28.7 million.

The remaining section of Highway 101 that still awaits widening work is the stretch from north Petaluma to Novato. The project, which is not currently funded, is estimated to cost $120 million in Sonoma County and $113 million in Marin County.

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