Replacement of the Highway 12 bridge spanning the Laguna de Santa Rosa at Sebastopol's eastern gateway is likely to present motorists with additional delays at an already tight bottleneck as construction gets underway this summer, officials said.

A Caltrans spokesman said every effort would be made to keep traffic moving smoothly when work begins June 15 on a new span for the busy east-west corridor.

But there will be times when only one lane of traffic is open — hopefully only at night, to reduce the impact on motorists, spokesman Allyn Amsk said.

Caltrans officials are hosting a public meeting on the two-year project in Sebastopol on Monday night.

City officials and some business owners said additional congestion is unavoidable during construction, given the traffic backups that already occur in the area.

The stretch of road carries an average of 23,200 vehicles daily, Caltrans officials said, citing 2012 data.

"It's just a daily traffic jam," said Juan Moya, who manages a Chevron service station on Highway 12 east of the bridge and often sees cars backed up in his direction.

The 220-foot span, first built in 1921, is being replaced because of structural deficiencies, including underwater scouring and erosion in the foundation, first discovered during a 2002 inspection, Caltrans said.

The $9 million replacement work will result in a wider bridge, with 8-foot shoulders and sidewalks at least 5 feet wide in each direction, improving pedestrian and bicycle access and safety along the roadway.

"I think it's going to be better for everybody overall, in the long run," said Darius Azarvand, whose family owns Sebastopol Liquor and Deli on Highway 12. "But it's going to hurt some of the smaller businesses in the short term, of course."

Construction crews will be operating under environmental restrictions related to the laguna's riparian habitat and other rare plant and wildlife safeguards, Amsk said.

Construction work is limited to a June-to-October window, roughly corresponding with the dry season.

Large trees removed from the area to the south of the bridge were cut down during the winter, to comply with federal law protecting migratory birds, officials said.

Ghilotti Construction Co. of Santa Rosa was awarded the contract for the upcoming work.

Crews are to begin building the southern portion of the bridge first and open it to traffic as soon as it's completed, likely by the end of the summer, Amsk said.

Next year, workers will demolish the old bridge and build the northern portion, with the southern span carrying traffic in both directions as construction proceeds.

Landscaping around the area will be completed in the third year, he said.

Barney Aldridge, owner and manager of The Barlow, a newly developed, 96,000-square-foot retail center featuring about three dozen eateries, tasting rooms, stores and work spaces at the eastern edge of town, said he had not been aware the bridge work was planned this summer.

But after commuting from Marin County through multiple major construction zones during the three years it took to construct The Barlow, he said he has a high regard for Caltrans' ability to keep traffic on track.

"I'm going to stay optimistic that they'll use the same diligence and care on Highway 12 that I've seen them use elsewhere," he said.