Napa County’s Bay Area-worst rating for bridge conditions should inch upwards with the Conn Creek bridge replacement scheduled to start this spring on busy Silverado Trail.
The Metropolitan Transportation Commission’s Vital Signs report says 13.9 percent of the bridge-and-overpass deck area in Napa County is “structurally deficient.” That is the worst rate among nine Bay Area counties and above the region’s 6.7 percent.
While “structurally deficient” can sound ominous, the classification doesn’t necessarily mean a bridge has a crippling defect. A Caltrans report said deficiencies noted during bridge inspections can be maintenance needs such as painting or filling in cracks.
“In the meantime, the bridge can be safely used by the motoring public,” the report said.
Conn Creek bridge along Silverado Trail east of Rutherford will be Napa County’s next bridge fix-it project. In this case, the remedy goes far beyond a patch job.
“The existing bridge has been affected by scouring of the creek bed, causing settlement and damage to its structure,” Caltrans spokesperson Janis Mara said in an email. “It is not possible to repair the damaged components.”
Rather, Caltrans will tear down the early 1970s bridge and build a new one at a cost of $8.3 million. Construction is to begin this spring and last into 2020. Caltrans plans to demolish and reconstruct the bridge in two sections, so one side is available to carry traffic while work goes on.
One lane will be open in each direction during most of the construction period, except during temporary closures, Mara said. There will be no shoulders.
A left-turn lane will be provided on southbound Silverado Trail for traffic turning east onto Sage Canyon Road, she said. However, traffic traveling north on Silverado Trail and traffic turning west onto Conn Creek Road will share a lane.
Caltrans and not the county is in charge of the work because the Conn Creek bridge is along a brief Highway 128 section of Silverado Trail.
The city of Napa will have an easier time fixing the five structurally deficient bridges within its limits. One of them is the Third Street bridge that was rebuilt over the Napa River for the flood control project only 17 years ago.
Caltrans inspects bridges every two years from top to bottom, city of Napa Deputy Public Works Director Eric Whan said. Sometimes, the deficiency is tiny cracks in the bridge deck that pose no safety threat.
“Concrete flexes, contracts, moves,” Whan said. “As vehicles drive across it, it flexes and moves. You will get little microscopic cracks that form. They are so small you’re not going to notice them.”
The Third Street bridge has these microscopic cracks in its pavement. Erasing them is not an elaborate process.
“We just have to do a deck treatment and it will be back to 100 percent,” Whan said.
Perhaps the county bridge in the worst shape is the Garnett Creek bridge on Greenwood Avenue near Calistoga. Cracked by the 2014 South Napa earthquake, this 1904 stone arch bridge is listed in the Vital Signs report as having a superstructure in imminent failure condition.
Napa County closed the bridge after the earthquake and is still evaluating whether it will be repaired or replaced, county Public Works Director Steven Lederer said. Work is to begin in 2022.
The county has other bridge repair projects in the works – Dry Creek Road over Dry Creek to begin construction in 2021 and Chiles-Pope Valley Road over Chiles Creek to begin construction in 2021. Plus, it is working to obtain Federal Emergency Management Agency funding to replace the bridge over a creek on Partrick Road that was damaged in the South Napa earthquake.
Further out are plans to work on Soda Canyon Road bridge over Soda Creek, Loma Vista Drive bridge over Soda Creek, Hardin Road bridge over Maxwell Creek, Conn Valley Road over Conn Creek and Berryessa-Knoxville Road bridge over Eticuera Creek.
Vital Signs didn’t count individual bridges to come up with Napa County’s 13.9-percent bridge deficiency rate. Rather, it looked at the county having 12,436 square meters of deck space on structurally deficient bridges out of 89,714 square meters of deck space overall.
There’s another way to look at the issue. Federal Highway Administration data for 2016 shows 12 of 150 Napa County bridges are structurally deficient. That’s 8 percent.
Napa County has company when it comes to bridge needs. The federal report stated that 1,388 out of 25,431 California bridges are structurally deficient, covering an area of 1.8 million square meters of bridge deck.
Perhaps the state’s and the region’s most famous bridge, the Golden Gate Bridge, is rated as structurally sound in the Vital Signs report.