When it comes to planning and executing construction, excavation, or infrastructure projects, accurate subsurface information is not a luxury — it’s a necessity. Failing to correctly identify what lies beneath the surface can lead to project delays, skyrocketing costs, serious safety hazards, and regulatory issues. That’s where utility locating and Subsurface Utility Engineering (SUE) come into play.
Although these two disciplines are often mentioned together, they serve different purposes and are applied at different stages of a project lifecycle. Understanding the Difference Between Utility Locating and SUE is vital for project managers who want to minimize risk, improve project efficiency, and ensure compliance with industry standards.
In this detailed guide, On The Mark Locators breaks down both practices — from definitions to practical usage — so you can confidently choose the approach best suited for your project.
1. What Is Utility Locating?
Utility locating is the process of identifying and marking the position of underground utilities such as water lines, sewer mains, gas pipelines, electrical conduits, fiber optics, and communication cables. It is primarily a field-based activity that provides real-time, on-site detection of buried infrastructure.
Key Features of Utility Locating
- Detection and Marking: Technicians use specialized equipment (like electromagnetic locators, ground-penetrating radar, and signal transmitters) to find utilities and mark them with color-coded paint or flags.
- Surface Level Information: Utility locating provides horizontal (and sometimes approximate vertical) locations of utilities but generally does not include detailed engineering data.
- Required Before Excavation: It is typically performed immediately before breaking ground to prevent accidental strikes during digging.
Why Utility Locating Matters
Without accurate utility locating:
- Crews risk hitting live utilities, causing injuries or fatalities.
- Projects may incur costly delays while damaged lines are repaired.
- Contractors and owners may face fines for regulatory non-compliance.
Utility locating is a reactive safeguard — a critical step that should be completed before any excavation, trenching, or drilling.
2. What Is Subsurface Utility Engineering (SUE)?
Subsurface Utility Engineering (SUE) is a higher level of investigative practice that involves the systematic collection, analysis, and depiction of subsurface utility data as part of a formal engineering process. SUE elevates utility information from basic detection to design-ready documentation.
What SUE Actually Does
SUE integrates both field and office processes to produce a utility map that is:
- Accurate
- Engineered
- Quantified for reliability
The goal of SUE is to reduce uncertainty in subsurface conditions, especially during the design phase of infrastructure projects. This reduces risks like design rework, utility relocation conflicts, and unforeseen costs.
How SUE Works
SUE typically follows a classification system based on confidence levels (e.g., ASCE 38-02 standards), which range from:
- Quality Level D (lowest confidence) – existing records and verbal recollections
- Quality Level A (highest confidence) – precise horizontal and vertical positions obtained through excavation verification
These classifications help stakeholders understand how reliable each piece of utility data is and plan accordingly.
3. Head-to-Head: Utility Locating vs. SUE
At a glance, both utility locating and SUE involve identifying underground utilities. However, the scope, purpose, accuracy standards, and project timing between the two are very different.
Purpose
- Utility Locating: Prevents utility strikes during excavation.
- SUE: Provides engineered utility data for design, planning, coordination, and risk mitigation.
Scope of Work
Feature | Utility Locating | SUE |
Horizontal & Vertical Positioning | Approximate | Precise |
Engineering Analysis | ❌ | ✔️ |
Documentation for Design | ❌ | ✔️ |
Used During Construction | ✔️ | ✔️ |
Used During Project Planning/Design | ❌ | ✔️ |
When Each Is Used
- Utility Locating: Typically used just prior to excavation or digging, often within days or hours before the work begins.
- SUE: Used earlier in the project lifecycle — during planning and design — so engineers and designers can make informed decisions.
Although utility locating can be part of a SUE program, it alone does not satisfy SUE requirements for engineered utility data.
4. Tools and Technology: What’s Behind the Detection
Both utility locating and SUE rely on advanced equipment, but the degree and integration of technology differ significantly.
Tools Used in Utility Locating
- Electromagnetic Locators: Detect metallic utilities by tracking signal transmission along conductive lines.
- Ground-Penetrating Radar (GPR): Uses radar pulses to image subsurface features, useful for both metallic and non-metallic objects.
- Signal Generators: Help trace utility lines by inducing a frequency signal that the locator can pick up.
These tools allow locators to mark utilities on the ground surface, often using colored flags and paint to indicate different utility types.
Tools Used in SUE
SUE uses the same detection tools, plus:
- Laser Scanning (LiDAR): For high-resolution 3D mapping of the surface and correlating subsurface data.
- Vacuum Excavation (Daylighting): Non-destructive potholing to verify precise positions.
- GIS & CAD Integration: Field data is processed into digital maps and engineering plans.
SUE blends traditional detection with engineering validation and documentation — resulting in a dataset engineers trust.
5. Project Stage: When Each Is Applied
Understanding when to use utility locating and when to apply SUE is essential for project efficiency and safety.
Utility Locating: Just Before Construction
Utility locating is often a last-step safety check that happens immediately before digging:
- Days or hours before excavation
- As part of daily pre-work procedures
- Right before breaking ground on individual segments
Its narrow timing makes it perfect as a safety precaution but limited for design insight.
SUE: Early in Project Lifecycle
SUE should be implemented early in planning and design so that:
- Utility conflicts can be identified and resolved before construction
- Design alterations are minimized
- Budgeting and permitting are more accurate
By investing in SUE early, project teams can save significant time and money downstream.
6. Cost, Risk, and Value: Why It Matters to Project Managers
When evaluating the Difference Between Utility Locating and SUE, cost vs. value is a key factor.
Cost Comparison
- Utility Locating: Lower upfront cost — primarily equipment and technician time.
- SUE: Higher upfront cost — involves specialized engineering, excavation verification, and data processing.
Risk Mitigation
Utility locating reduces immediate field risk, but SUE goes a step further by:
- Identifying unknown utility conflicts
- Reducing design rework due to unforeseen subsurface conditions
- Improving schedule certainty
ROI and Long-Term Savings
While SUE costs more initially, the return on investment is often greater due to:
- Fewer change orders
- More predictable construction timelines
- Lower risk of utility damage liability
In many large or complex projects, the cost of unknown utilities far outweighs the cost of a comprehensive SUE investigation.
Conclusion
Both utility locating and Subsurface Utility Engineering are indispensable in the world of construction and infrastructure development — but they are not interchangeable.
- Utility Locating is your frontline defense against utility strikes during excavation. It is reactive, focused, and time-sensitive.
- SUE is a proactive, engineering-driven process that provides accurate data for planning, design, and risk mitigation.
As a project manager, understanding the Difference Between Utility Locating and SUE empowers you to make strategic decisions that optimize safety, timeline, and budget.
At On The Mark Locators, we believe that quality utility data is the foundation of every successful project. Whether you need detailed SUE services for design or accurate utility locating right before excavation, our team delivers the precision and insight you need to build with confidence.
By integrating both practices at the right stages of your project, you’ll not only protect your workforce and assets but also elevate your project outcomes — from concept to completion.