Nevada County to ID bridge repairs
August 3, 2007
NEVADA CITY ” Two unrelated bridge collapses this week may have some drivers leery about the safety of local spans.
Nearly 13 percent of the nation’s bridges were classified as “structurally deficient” as of 2004, according to a report issued by the Federal Highway Administration and posted on the Web site consumeraffairs.com Thursday.
Nevada County’s bridges generally are “safe,” but need work, local officials said Thursday.
“Overall, they’re in decent shape. I think they are certainly safe for what they were designed for,” said John Rumsey, senior civil engineer for the county.
The county public works department is in the process of putting together a capital improvement program that will identify roads, bridges and other projects that need work in the next five years, Rumsey said. The plan will go before the county Board of Supervisors in two to three months.
The assurances came a day after a bridge collapsed during rush hour in Minneapolis, killing at least four people and leaving at least 30 missing, according to The Associated Press. And on Tuesday, a delivery truck driver and construction worker were injured when a highway overpass under construction collapsed in Oroville.
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The California Department of Transportation inspects 24,000 bridges in the state every one to two years and maintains 12,000 along state highways and interstates, Caltrans spokeswoman Shelly Chernicki said.
California is rated seventh in the nation for the quality of its bridges, which have an average age of 40 years, Chernicki said.
“Our bridge department and personnel are the best in the country,” Chernicki said. “We have bridge maintenance crews. They are out there day to day. If they see a problem, we react very quickly.”
Nevada County is responsible for 71 bridges, and half of those are more than 50 years old, Rumsey estimated.
“There are a number of bridges that need some type of work,” Rumsey said. “After a period of time, materials get tired and need to be replaced,” he said.
In the past year, planks were replaced on the bridge at Purdon Crossing, which also is slated for repainting soon. A bridge is being retired across Squirrel Creek near Rough and Ready Highway and will be replaced by a box culvert, Rumsey said.
Old river crossings with truss support structures like those at Edward’s Crossing and Purdon’s Crossing have posted load restrictions of three tons, Rumsey said. One passenger vehicle weighs about three tons. Traffic volume is low on those bridges, Rumsey said.
Last September, County Supervisor John Spencer questioned money spent to paint the Purdon Crossing Bridge because he thought it was time to consider replacing the bridge to allow the safe passage of heavy equipment such as fire engines.
“Fire could happen at any time,” Spencer said.
The cost to replace the bridges is high, especially if engineers try to capture the historical integrity of the old crossings. In 1996, it cost $3.5 million to replicate the Pine Street bridge, said Nevada City’s longtime engineer, Bill Falconi. The weight restriction of the old bridge allowed only one car to cross at a time.
“It was getting dangerous,” Falconi said.
Environmental constraints along the South Fork Yuba River delay the replacement of old bridges, Rumsey said. Federal money used to finance building new bridges usually requires widening roadways, a difficult feat for winding, narrow roads like North Bloomfield and Lake Vera Drive, Rumsey said.
Replacing historic bridges with stronger, modern engineering is inevitable and can be done while preserving the original look of the architecture, Falconi said.
“Everything wears out over time. Nothing is forever,” he said.