ILL 159 Road Improvements Project: A Case Study

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The ILL 159 Road Improvements project in Collinsville, IL, required meticulous planning and execution to update the roadway infrastructure without disrupting the vast network of underground and overhead utilities.

Undertaken by a Subsurface Utility Engineering (SUE) consultant for the Illinois Department of Transportation (IDOT) District 8, this case study highlights the project's scope, the strategies employed to map utilities, and the outcomes of integrating SUE practices into the project planning process.

Project Scope and Overview

The consultant was tasked with the ambitious goal of designating over 178,000 feet of utilities, encompassing both underground and overhead components.

To manage this extensive workload and keep the high-profile project on schedule, six field designating teams were mobilized, providing continuous feedback and updates to IDOT.

Methodologies Employed

Early Engagement of QL-B Services
Uniquely, all Quality Level B (QL-B) services, which involve the use of surface geophysical techniques to infer the presence of utilities, were performed prior to the development of background mapping.

This proactive approach allowed for the identification of potential utility conflicts early in the project, facilitating more informed planning and design decisions.

Sewer Mapping Techniques
Sewer mapping presented its own set of challenges, requiring access to manholes and the insertion of composite core reels to trace the path and characteristics of sewer lines accurately.

This method ensured a detailed understanding of sewer utility locations and conditions, critical for avoiding disruptions during construction.

Test Hole Excavation
To resolve potential utility conflicts identified during the QL-B phase, a total of 56 test holes were excavated.

These test holes provided QL-A data, the highest level of accuracy in utility mapping, offering precise depth and elevation information for utilities at conflict zones.

This data was instrumental in making critical design adjustments.

Challenges and Solutions

The project's success hinged on the ability to accurately map a dense network of utilities within a busy urban environment.

The early execution of QL-B services, coupled with strategic test hole excavations, allowed the team to navigate these challenges effectively.

Continuous communication and coordination with IDOT ensured that project adjustments were made promptly, keeping the project on track.

Impact and Outcomes

The ILL 159 Road Improvements project stands as a testament to the value of integrating SUE practices into infrastructure projects.

Through detailed utility mapping and strategic planning, the project was able to proceed with minimal disruptions to existing utilities, ensuring the safety and efficiency of the construction process.

The successful designation of utilities and resolution of conflicts through QL-A data exemplifies the project's commitment to precision and proactive problem-solving.


The meticulous approach to utility mapping and conflict resolution employed in the ILL 159 Road Improvements project underscores the critical role of SUE in modern infrastructure development.

By prioritizing early and accurate utility designation, the project minimized potential delays and costs associated with utility relocations or damages, setting a benchmark for future road improvement projects in urban settings.

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