US20B Stockham & US20 “Peanut” Roundabout Rigby, Idaho

Roundabout: Project Success: The project was successfully fast-tracked to accommodate an aggressive schedule set by ITD and their partners.

Project Background and Need

The existing “T” intersection geometry created safety concerns and operational challenges, particularly for vehicles accessing adjacent businesses and for large trucks navigating tight turning movements. With rapid growth in the area and the intersection serving farm equipment, school buses, freight trucks, and passenger vehicles, ITD and the City of Rigby identified the need for a longterm solution that improved safety while minimizing delay for through traffic.

Horrocks partnered with ITD and a private development firm to develop a roundabout solution that addressed these deficiencies while fitting within constrained rightofway and utility limitations.

Innovative Design and Visualization

As the first roundabout on ITD’s network, it was critical that the design functioned correctly and that its intent was clearly understood by stakeholders, reviewers, the public, and the contractor. Horrocks used advanced 3D modeling throughout design to visualize the roundabout geometry, drainage, utilities, and grading.

The 3D design model was developed into a fully integrated AMG construction package, allowing the contractor’s equipment to be guided directly from the digital model. This approach eliminated traditional construction staking—only one temporary control stake was required—and reduced the risk of errors, delays, and rework. Models were also shared with ITD and construction staff to support inspections and field verification.

Accommodating Oversized Vehicles

Nicknamed the “Peanut” Roundabout due to its unusual shape, the design generated early concern from the public and stakeholders about how large trucks would navigate the intersection. To address these concerns, Horrocks conducted extensive vehicle tracking analysis and supplemented it with a realworld field test.

A fullscale mockup of the roundabout was painted in a local trucking lot, where typical vehicles and a longhaul WB67 truck were driven through the layout to evaluate speeds and trailer tracking. The results confirmed the computer analysis and demonstrated that the roundabout safely accommodated oversized vehicles. Aerial video from the test became a valuable publicoutreach tool, helping stakeholders visualize operations and build confidence in the design.

Survey, Utilities, and RightofWay

Horrocks provided topographic, utility, and rightofway surveys to support the design. LiDAR data was collected to calculate sag heights of highvoltage transmission lines crossing the project, and survey data was processed into a detailed terrain model. ROW boundaries were retraced to ensure the roundabout fit within property constraints. Utility layouts were modeled in 3D and shared through Google Earth to improve coordination and communication with stakeholders.

Public Outreach and Education

Because roundabouts were new to the community, extensive public outreach was critical. Horrocks supported efforts to educate residents and stakeholders on how the roundabout would function and why it was the preferred solution. Visualization tools, videos, and field demonstrations helped translate complex traffic concepts into easily understood, realworld examples.

Project Outcomes and Recognition

• Successfully delivered ITD’s first roundabout

• Improved access to local businesses while minimizing traffic delay

• Enhanced safety and operational performance for all vehicle types

• Implemented innovative AMG construction delivery using 3D models

• Eliminated traditional construction staking, improving efficiency and accuracy

• Fast tracked delivery to meet an aggressive ITD schedule
  

Lasting Value

The US20B Stockham “Peanut” Roundabout set a new precedent for innovative intersection design in Idaho. Through advanced modeling, collaborative problemsolving, and proactive public engagement, Horrocks delivered a solution that balanced safety, mobility, constructability, and community trust. The project not only solved longstanding operational challenges but also expanded ITD’s toolkit for future intersection improvements across the state.