Friday, August 8, 2014

ITD unveils tentative design for new bridge

Construction planned for 2016 on span south of Ketchum

Express Staff Writer

This ITD graphic shows the preliminary design of a new bridge to be built in 2016 over the Big Wood River south of Ketchum. The new bridge is wider, longer and higher than the existing structure and will have passage areas on either side for large wildlife.
Courtesy graphic

    An Idaho Transportation Department planning and design team has taken into consideration animals and aesthetics in the preliminary design of a new bridge planned for construction in 2016 to carry state Highway 75 across the Big Wood River south of Ketchum.
    “It’s important to the local community and to the valley as a whole as to what the bridge looks like,” Mike Pepper, public involvement lead for the project, said at a Thursday meeting of the Blaine County Regional Transportation Committee. “With all that said, the bridge still needs to work.”
    The new bridge will be wider, longer and higher than the bridge that now crosses the river just north of St. Luke’s Wood River hospital. With four traffic lanes, ITD intends that the bridge tie in smoothly with four lanes of traffic both to the south and north of the structure.
    The four lanes to the south are currently under construction as part of another ITD highway construction project. The four lanes to the north will be built as part of the bridge replacement project and will extend north to the Highway 75 intersection with Elkhorn Road.
    Both projects are part of an ITD Highway 75 expansion plan that if finished would widen Highway 75 from Timmerman Junction south of Bellevue all the way north to Saddle Road in northern Ketchum, a distance of 27 miles. Total expansion is expected to cost well over $200 million, but ITD thus far has only $27 million earmarked for funding from the Federal Highways Administration.
    ITD has determined that the $27 million is enough to pay for the construction project now under way, the bridge project planned for 2016 and for federally required wetlands mitigation for the entire 27-mile corridor.
Bridge presentations
    Members of the bridge project planning and design team, including Pepper, of KMP Planning in Twin Falls, ITD Project Manager Steve Hunter and engineers with Parametrix Inc., of Boise, have been making the rounds in Blaine County this week to explain the project to officials and the public at local public meetings. The meetings are in advance of a public open house scheduled for Aug. 26 in Ketchum (see sidebar).
    At Thursday’s Regional Transportation Committee meeting, Pepper said that during bridge construction, which is expected to last into 2017, two lanes of traffic will be kept open at all times. He said construction of the new bridge will begin on the west side. Once that’s finished, traffic will be diverted to the west side of the new structure while construction takes place on the east side.
    According to the preliminary design, the new bridge will be 74 feet wide with four 12-foot lanes. It will also have a 4-foot wide median and “adequate shoulders” on either side.
    In addition to being wider, the new bridge will be 30 feet longer than the existing structure. It will also be 3 feet higher, a provision that will help with wildlife passage.
    “You’ll see in the elevation, there’s a lot more room for a wildlife path,” Pepper said. “It will provide a substantial area for large animals to get through that area.”
    Pepper said further that the wildlife passages on either side of the river will be kept free of vegetation to give animals a “comfort zone” so that they will use the passages rather than trying to cross on the highway.
    ITD’s Hunter pointed out that during high water events that wildlife passages on either side of the river will likely be flooded.
    “Both passages will be closed in high water,” he said.

Open house
An open house is scheduled for Tuesday, Aug. 26, to explain to the public the design and processes involved for a new bridge over the Big Wood River south of Ketchum. The open house will be held from 5-7 p.m. at the Kentwood Lodge, 180 S. Main St., in Ketchum. An Idaho Transportation Department planning and design team for the project will be available to answer questions and take public comments.

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