Jct. US-20 and SH-33 & Jct. US-20 and University Boulevard Diverging Diamond Interchanges | Rexburg, ID

Project Overview

Horrocks collaborated with ITD to retrofit two critical interchanges in Rexburg, US-20/SH-33 and US20/University Boulevard, by converting traditional diamond interchanges into DDIs. These projects significantly improved mobility, safety, and reliability along US-20, the primary access route serving Rexburg residents, regional travelers, and approximately 22,000 Brigham Young University-Idaho students. The improvements preserved existing bridge structures while modernizing operations to meet current and future traffic demands.

Services Provided:

• Roadway and traffic design, including signals, signing, striping, and illumination

• Value engineering, constructability reviews, and design optimization

• Drainage and utilities design

• Noise studies and right-of-way support

• Construction staging and traffic control planning

• Signal timing support and real-time design assistance during construction

• Landscaping, aesthetics, and gateway feature coordination

• Field engineering support and incorporation of agency and public feedback into final design

Challenges

The existing interchanges experienced severe congestion and unsafe queuing, especially for left-turn movements crossing US-20, with peak delays approaching 5 minutes. As the only access points to US-20 for Rexburg and surrounding areas, maintaining mobility during construction was a critical concern.

Horrocks supported ITD in implementing innovative DDI configurations that eliminated conflicting left turns, reduced signal phases, and improved operational efficiency while fitting entirely within four existing bridge structures. During construction, a bridge alignment constraint was identified that required rapid redesign. Our team quickly modified roadway geometry without affecting schedule or budget.

Public input strongly favored shorter, more intensive construction periods over extended lane restrictions. In response, Horrocks helped shift to an accelerated construction strategy that included temporary interchange closures and comprehensive detour planning coordinated with the City of Rexburg and Madison County. This approach allowed both interchanges to be constructed within a single season.

Successes

• Converted two high-volume interchanges to DDIs while preserving existing bridge structures

• Reduced peak delays from approximately 5 minutes to 45 seconds

• Completed construction one year ahead of schedule

• Achieved approximately $40 million in combined cost savings through optimized design and accelerated delivery

• Successfully incorporated Idaho’s first hydrogen fuel-cell battery backup systems for traffic signals, improving resilience and sustainability

• Integrated public input into operational, aesthetic, and construction decisions

• Enhanced safety, mobility, and reliability along a vital regional corridor

Through close collaboration with ITD, local agencies, and the community, Horrocks delivered transformative, cost-effective infrastructure that supports Rexburg’s growth while improving quality of life.