I84 Corridor Improvements – SH-44 Interchange to Karcher Rd. Interchange Canyon County, ID

Planning, Environmental, and Design Leadership

Horrocks led a multidisciplinary team to complete traffic and safety studies, corridor planning, and environmental documentation for more than eight miles of I84. The work included alternatives development and recommendations for additional generalpurpose lanes, bridge reconstruction, and interchange improvements. Indepth traffic analysis identified operational constraints, informed corridor limits, and guided future design decisions. A 2050 designyear traffic sensitivity analysis ensured the proposed improvements would remain effective over time.

Supporting services included survey and rightofway mapping, environmental resource fieldwork, hydraulic screening, and development of alignments, typical sections, and interchange alternatives. Extensive public involvement and coordination with ITD and local agencies supported streamlined decisionmaking.

Urban Corridor Challenges and Solutions

As I84 passes through Caldwell, development along the corridor has intensified, limiting construction space and increasing sensitivity to traffic and community impacts. Maintaining two lanes in each direction on I84 and preserving circulation on Centennial Way, 10th Avenue, and other local routes was essential.

Traffic Maintenance and Phasing:
Horrocks developed detailed, ITDcompliant construction phasing and traffic control plans that maintained interstate and local traffic while creating safe, efficient work zones.

Noise Impacts:
With residential neighborhoods adjacent to the corridor, traffic noise was a key concern. Based on detailed noise analysis, a noise wall was incorporated along a portion of the project to mitigate impacts.

Stormwater and Environmental Constraints:
Stormwater from I84 and nearby City of Caldwell streets historically discharged directly to the Boise River through a combined system. Horrocks designed a new stormwater system that separates ITD and city facilities, incorporates detention and treatment, and uses hydrodynamic separators to improve water quality prior to discharge.

Utilities and Irrigation:
Numerous utility conflicts and historic irrigation facilities required preservation. Horrocks used advanced 3D pipe modeling to resolve vertical conflicts and coordinated closely with irrigation districts to maintain uninterrupted operations.

Project Successes

• Delivered three PS&E packages resulting from the environmental study and preliminary design

• One PS&E package delivered on an accelerated schedule and $1.279 million under budget

• Successfully separated ITD and City of Caldwell stormwater systems while improving treatment prior to discharge

• Improved safety and operations through interchange reconfiguration, including removal of a loop ramp at the 10th Avenue Interchange to reduce weaving between closely spaced interchanges

Corridor Improvements by Segment

• Centennial Way to Franklin Road (Caldwell): Horrocks led the reconstruction and widening of I84 through three closely spaced interchanges, including replacement of the 10th Avenue Interchange bridge.

• Franklin Road to Karcher Road: Horrocks provided roadway and drainage design for two miles of I84 and construction staging, traffic control, ITS, and illumination design for four miles. Improvements included rigid pavement reconstruction, median barrier retaining walls, and addition of a third lane in each direction.

• Karcher Road IC to Franklin Boulevard IC (Nampa): Horrocks provided construction staging, traffic control, signal, ITS, and illumination design for this threemile segment. The project includes rigid pavement reconstruction, an additional generalpurpose lane, auxiliary lanes in each direction between Karcher Road and Franklin Boulevard, evaluation of auxiliary lanes between Northside Boulevard and Franklin Boulevard, and replacement of four structures.

• Caldwell to Karcher Environmental Evaluation: Horrocks prepared traffic studies, corridor planning, and environmental clearance documents for I84 between Caldwell and Nampa. Two environmental evaluations were completed—one for mainline I84 improvements and a separate evaluation for the Middleton Road and Ustick Road overpasses.

Lasting Value

Through technical expertise, innovative problemsolving, and close collaboration with ITD and local stakeholders, Horrocks delivered durable, forwardlooking transportation solutions that support regional mobility, community needs, and environmental stewardship along one of Idaho’s most important corridors. Horrocks is currently providing CE&I services for Centennial Way Interchange to Franklin Rd. Interchange.