I-84 Meridian Road Interchange

The I-84 Meridian Interchange in Meridian, Idaho, was built in 1965 to accommodate the approximately 12,000 vehicles driving along the highway each day. Today, the highway corridor sees more than 128,000 vehicles per day, and the aging interchange at Meridian Road could simply no longer handle the volume of traffic.

Beginning in 2012, the Idaho Transportation District (ITD) contracted with Parametrix and an experienced team, including GeoEngineers, HNTB and T-O Engineers to design the I-84 Meridian Interchange Project. Concrete Placing Company (CPC) completed the construction in 2015, following the design phase. GeoEngineers’ role on the team consisted of performing geotechnical investigations, preparing ITD Materials Phase Reports to support earthwork, foundation, retaining wall, seismic and pavement design.

Once approved, the Meridian Interchange progressed on a rapid timeline. The bulk of GeoEngineers’ geotechnical investigation and design work had to be completed in a 9-month window before construction could begin.

The new I-84 Meridian Interchange consists of a two-span, concrete girder bridge using a single point urban interchange (SPUI) design with a single traffic light on the overpass controlling all traffic on Meridian Road passing over I-84. The updated interchange features three through lanes in each direction, two turning lanes each direction, plus additional east- and west-bound lanes on I-84 under the overpass, two left-turn lanes on each exit ramp, new storm-drain systems, sidewalks and bicycle lanes. The new interchange will be able to handle 284,000 vehicles per day to accommodate future growth in Meridian, Idaho.

Approach

• GeoEngineers performed an initial geological reconnaissance and review of the existing structures to establish initial project recommendations.
• Our team performed a life-cycle cost analysis of pavement materials to determine which materials and compositions would be most cost effective to build and maintain on the various soils of the interchange site. Our analysis indicated a combination of flexible and rigid pavement designs.
• A detailed subsurface soil investigation showed that the soil conditions would safely support the structure using shallow spread footings rather than deeper foundations, saving significant construction costs.
• Our team designed the shallow foundations constructed below the mechanically stabilized earth (MSE) walls supporting the approach embankments. The bridge columns at the abutments extended through the reinforced zone of the MSE walls.
• GeoEngineers also provided groundwater monitoring and preliminary dewatering recommendations for the site.

Results

GeoEngineers and the design team worked together to complete the I-84 Meridian Interchange on time and on budget, relieving traffic congestion and providing an efficient interchange design that will accommodate and encourage local economic growth for decades to come.