I-84 Corridor

The I-84 Corridor improvements were intended to improve mobility, increase safety, and benefit the regional economy. The existing interstate could no longer accommodate current traffic volumes at peak periods of the day. As the Treasure Valley continues to grow, congestion in this corridor will increase. Parametrix led the design of over $360M in improvements to reconstruct and widen I-84 between Caldwell and Nampa. The work involved six interchanges (including diamond, single point urban, and partial cloverleaf); adding a third lane in each direction of I-84; adding auxiliary lanes in each direction between the interchanges; replacing the Northside interchange with a single point urban interchange (SPUI) for safer and more efficient travel; rebuilding the Karcher Road overpass, railroad, and irrigation canal bridges, and the Mason Creek structure; and widening the eastbound off-ramp at the Franklin Boulevard interchange and modifying signals to allow two left-turn lanes onto the westbound on-ramp.

Phased implementation of improvements in this 10-mile corridor required simultaneous delivery of multiple PS&E packages on accelerated design schedules with overlapping construction contracts; multi-year traffic and level of service analysis; complex environmental investigations, documentation, mitigation, and permitting; interchange modification reports; and extensive public and stakeholder outreach programs.



Idaho Transportation Department

Caldwell to Nampa, ID, I-84 Corridor, Caldwell to Nampa, ID
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