I-82 South Union Gap Interchange Construction Ramps
Design-Build

This design-build project completed the I-82/US 97 interchange, creating greater connectivity between the city of Union Gap and two major highways, I-82 and US 97. The new Main Street to westbound I-82 on-ramp included a 2-span pre-stressed, precast concrete girder bridge founded on concrete spread footings over I-82. Limited right-of-way due to existing interchange alignments, wetlands, and adjacent railroad property proved challenging.

Hamilton’s expertise and perseverance led to developing innovative design and construction of the new I-82 westbound on-ramp. This provided the City a direct connection to westbound I-82 from Main Street, which previously did not exist.
Additional structure work included cast-in-place concrete retaining walls, structure earth walls, geosynthetic reinforced slopes, and existing bridge rehabilitation. 

Hamilton’s constructability reviews produced two Alternative Technical Concepts (ATC) that revised a substantial portion of the interchange alignment and brought significant value to the project and WSDOT. The revised design of the eastbound I-82 off-ramp eliminated impacts to wetlands and reduced the size of the retaining walls by approximately 3000 SF. The revised design of the westbound I-82 on-ramp provided a more efficient, streamlined roadway geometry and eliminated a hazardous left turn against oncoming traffic.

The design-build process allowed for a high level of detail and engagement between Hamilton and WSDOT.  Design related hurdles were encountered when Hamilton’s ATCs were advanced with the collaborative efforts of WSDOT. The unique nature of several design elements of the new ramp alignments required extraordinary coordination as they often fell outside of standard design guidelines.
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The project team maintained an exceptional level of open and transparent communication from the field level through the project management staff and onward to the senior level management. Members of both Hamilton and WSDOT were engaged in information gathering meetings before project advertisement and stayed onboard through to project substantial completion. This created trust and effective partnering.

Major Project Elements

• Design-Build
• Complex Staged Highway Work
• Widening Highway Structures
• Cutting/Filling Walls
• Pavement Rehab
• Constructing Surface Streets
• Traffic Signals/ Ramp Meters
• Drainage/ Water Quality Improvements
• DBE/Diversity
• Partnering
• Maintenance of Multimodal Traffic
• Constructability Reviews
• Proposed/Approved Alternative Technical Concepts (ATC)
• Innovative Staging/Traffic Management
• Stakeholder/ Community Collaboration
• Multiple Sites
• Coordination with Neighboring Projects