With the completion of a $190,000 engineering study, the future is now less uncertain for four elderly but vital two-lane, single-span bridges in Woodside on Mountain Home, Kings Mountain, Portola and Old La Honda roads.
The two arched bridges across Mountain Home and Kings Mountain roads have been judged historic and should be rehabilitated, and the other two replaced at an overall cost of around $3.8 million, according to a staff report to the Town Council.
The council considered the report on Nov. 18 and gave the go-ahead to staff to seek federal funding for the work. In combination with maintenance needed on the town's storm drain system and completion of the safe-routes-to-school project, the town's infrastructure work is expected to take five to 10 years to complete, Town Engineer Paul Nagengast said.
The council is planning a study session to discuss the town's infrastructure and its upkeep if state and/or federal funds do not come through. The town learned in the fall, for example, that it did not win a grant of $855,000 to construct a new multi-use path along the south side of Woodside Road between the school and Roberts Market.
The town could have accepted federal money to simply replace the bridges, but at a cost to rural ambiance: the bridges would have been much wider. The council commissioned the engineering study to determine ways to have the bridges meet current standards without losing the charm they have acquired over a century of use.
A detailed analysis of their actual condition improves the chances for federal funding without the widening requirement, Mr. Nagengast said.
The arched bridges have structural deficiencies, the report says, and lists options for rehabilitating them. The recommended fix, at a cost of about $1.68 million for the two bridges, would fit each bridge with a curved structural steel plate under the arch and extend their lives by at least 50 years, the report says.
The Portola Road bridge over Alambique Creek is problematic in that the alignment of the bridge's north approach does not meet federal standards for a bridge with 3,000 vehicle crossings a day. Realignment may be complicated in that it's not clear where the public right-of-way begins and ends, Mr. Nagengast said.
This bridge, with a recommended fix that would run $1.16 million, will be the most challenging in terms of getting federal funding, he said. "They're going to want a wider bridge," he said.
While there are lower cost options, the federal government puts a high priority on safe infrastructure, said Carolyn Davis of Quincy Engineering, the Sacramento firm that did the analysis. "When you have a bridge that's this old, you typically don't want to invest a lot of money in (repairing) it," she said.
Resident Thalia Lubin, a member of the town's History Committee, said she wasn't terribly concerned about preserving this bridge. "It's the least culturally significant," she said.
Covered by moss
The bridge on Old La Honda Road has the highest priority, Mr. Nagengast said. The California Department of Transportation recently found "extensive deterioration" on the girders underneath the bridge side rails. In response, the town painted new white fog lines to narrow the bridge lane and keep traffic away from the edges, Mr. Nagengast said.
This bridge, thought to have been built in the 1920s as part of the August Schilling estate, is surrounded by a facade of sorts. There are artificial boulders alongside, covered with real moss, and an artificial grotto under the bridge. The side rails, also moss-covered, are a feature the council should consider salvaging, restoring or recreating on the new bridge, Mr. Nagengast said.
"The point is, we want to recreate how you currently enter the neighborhood," he told the Almanac. "That's what we don't want to lose." As for the "boulders" and the grotto, the environmental review process will dictate whether those elements are kept or not, he said.
Replacement options range from $920,000 for a concrete culvert to $1.25 million for pre-cast concrete; all would extend the bridge's life by at least 75 years. A key question will be whether the bridge would be closed to traffic during the work, and if so, for how long.
Quincy's analyses was based on bridge records, on-site inspections, ground-penetrating radar and the effects of stream-bed erosion. The engineering report included load-bearing ratings, which vary according to the number of axles on the truck.
Under current standards, any of these bridges should be able to handle a dump truck weighing up to 25 tons, a commercial trailer truck of up to 36 tons, and a tandem trailer truck of up to 40 tons.
According to the study, none were close to the stated capacity, but all had plenty of life left in them. The Mountain Home Road bridge is rated 12 tons, 19 tons and 23 tons, respectively, but can serve for 20 more years, the report says.
The Kings Mountain Road bridge also has 20 years left in it, but has the lowest rating: 3 tons for all truck categories. The Portola Road bridge can serve for another 10 years and is rated at 6, 10 and 12 tons, the report says.
Despite their low ratings, these bridges can handle heavier loads because their deterioration is likely to be gradual. The ratings specify loads that "have been determined to safely cross without accelerating deterioration," Mr. Nagengast told the Almanac. "We try to reroute construction traffic away from the bridges (but) we don't have bridge police," he added.