I-84 Snake River Twin Bridges
Key Number: Westbound - 11239, Eastbound - 12955
Project Number: A011(239), A012(955)
The Idaho Transportation Department (ITD) is planning a replacement of the I-84 Snake River Twin Bridges between Minidoka and Cassia Counties near the Declo Interchange at about milepost 216. The bridges are a critical link to interstate travel through the area. Nearly 18,000 vehicles use this portion of roadway each day and the volume is predicted to nearly triple in the life of the future bridges.
The current structures are located 8 miles east of Burley. They were built in 1960 and reconstructed in 1976. Each bridge is a concrete, stringer/girder bridge with 24 spans. The total length of the structure is 981 feet, with a maximum span of 40 feet. The width is 31.5 feet and 34.1 feet, curb-to-curb and out-to-out, respectively. The prestressed stringers/girders at the east end are cracked and have been repaired.
The Snake River is a critical concern and will require a biological assessment. A cultural resources study will be performed on the existing structure and surrounding land. Hydraulic and scour analysis will also need to be completed.
The project intends to replace the westbound Snake River bridge on I-84 during the 2015 construction year. The westbound on-ramp at the Declo interchange (Exit 216) may be redesigned and be longer in order to improve traffic safety. The bridges will be built to accommodate three lanes to increase capacity and allow for improved merge capabilities of the ramps. Span lengths and bridge types will be analyzed to find an economical structure that provides for all the environmental concerns.
The eastbound Snake River bridge is being considered for replacement in 2016 and will go through similar environmental, structural, and design analysis prior to construction.
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District 4 Public Information
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