Depicting Subsurface Utilities in Highway Design Plans
Last updated September 27, 2026
The utility lines on a highway plan set come from owner records, geophysics, and a few test holes, and they are not equally reliable. The engineer of record answers for all of them, and most of that data arrives from other people's work. The course starts with the four ASCE 38-22 quality levels and what each one claims about a buried line, then covers the detection and excavation methods behind them and the site conditions where each method falls short. It walks through scoping and scheduling an investigation, including how several state DOTs time it and what the published return-on-investment figures can and cannot support. It then turns to the plans themselves: line styles and metadata, noting where a search turned up nothing, out-of-service versus abandoned lines, and conflicting records. The final sections classify utility conflicts and track them to resolution, then follow the plans into the bid package, the State's utility statement at federal construction authorization, and the main project delivery methods. Material draws on NCHRP Research Report 1180, TxDOT-sponsored utility investigation research, SHRP2 R15B conflict management guidance, and 23 CFR Parts 645 and 635.
Learning Objectives
Interpret utility quality levels on a plan set, including what each level claims, who may assign it, and how long it holds.
Review a utility investigation deliverable against the methods used and the site conditions they worked in.
Scope and schedule a utility investigation so the data arrive while the design can still respond.
Carry utility conflicts through to the contract documents, from classification and resolution to the State's utility statement when federal construction authorization is requested.
BasePDH | Course 022 | 2 Professional Development Hours
Depicting Subsurface Utilities in Highway Design Plans
Introduction
The utility sheets of a highway plan set show the existing and proposed utilities within the project, and the space available for relocation or adjustment (Section 4.1) [1]. Producing the depiction takes investigation, documentation, evaluation, and communication directed at the needs of the plans' users [1], who include utility coordinators; designers in the utility, highway, structural, drainage, traffic, and environmental disciplines; construction project managers and contractors; asset managers; and utility owners and their contractors [1].
A utility conflict is a clash involving a utility facility, whether with other infrastructure, a required buffer, construction activity, or a regulation [1]. The design team finds conflicts during design, and a conflict found while the design is still open may be resolved by changing the design instead of moving the utility. Utility installations encountered unexpectedly during construction either had no information about them or were shown in the wrong place on the construction plans [3].
The depiction generally develops through preliminary and detailed design, as investigation is procured in stages and conflicts are reassessed on each round of data. The completed depiction goes to bidders with the contract documents at the end of design, and the State reports the status of utility work to the Federal Highway Administration (FHWA) before construction is authorized [4].
Utility owners supply records and take part in reconciling data sources that disagree [1]. Subsurface utility engineering (SUE) is the specialty practice of civil engineering's utility engineering branch that includes the investigation, analysis, judgment, and documentation of existing utility networks, resulting in achieved quality levels assigned to nonvisible segments and features [1]. A SUE provider is a licensed professional with working knowledge of shallow-earth geophysics, engineering surveying, utility construction and design, utility conflict identification, and utility risks [1]. The engineer of record is the licensed professional engineer who takes ultimate technical responsibility for the project, including the depiction (Section 4) [1].
A depiction is often built largely on others' data, and owner records, surface geophysics, and test hole exposure each support a different degree of confidence in a drawn line. The plans have to show which lines were measured, which were detected, which came from records, and where utilities were looked for and not found.
1. Utility Quality Levels
Each nonvisible utility segment and feature a SUE investigation covers carries a utility quality level, on the deliverables and the design plans built from them. SUE providers typically work under contract to state departments of transportation (DOTs) and produce certified and stamped deliverables, and some DOTs require prequalification [1].
A utility quality level is a value the professional assigns to a utility segment or subsurface utility feature to identify the relative, nonquantifiable uncertainty of its existence and actual location against its documented location [1]. A utility segment is a continuous portion of a utility over which the quality level is constant and the attributes other than depth are substantially identical, and a utility feature is a physical component such as a valve, vault, or transformer, above or below ground [1]. The value is judged on the source, precision, consistency, collection methods, and interpretation of the data, in context with the other information the professional then holds [1]. Because the uncertainty is nonquantifiable, a quality level is the professional's judgment of a line's reliability, not a measured distance between line and utility. Each survey tolerance in Section 1.3 attaches to a named measurement, and only at QL A does one attach to the buried utility itself, and then only to the portion exposed.
The definition comes from ASCE 38-22 (ASCE/UESI/CI 38-22, Standard Guideline for Investigating and Documenting Existing Utilities), and this course states the standard's definitions as NCHRP Research Report 1180 quotes them [1]. The earlier edition is ASCE 38-02 (CI/ASCE 38-02, Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data). Report 0-6631-1 is the Texas A&M Transportation Institute study for the Texas Department of Transportation (TxDOT) and FHWA; most Texas providers it interviewed used ASCE 38-02 as their guideline [2].
1.1 Sources of Utility Information
A utility record is documented information from owners or others describing a utility system, potentially including location, and such records tend to vary in age, accuracy, and completeness [1]. An as-built records the actual, final location, dimensions, and attributes of an installed utility, reflecting changes made during construction rather than recreating the design plans [1]. Information on existing utilities comes from these sources [1]:
- Records: utility owner records; DOT or agency records, including permits and project as-builts; the recollections of utility staff; and markings placed through One Call, the state damage-prevention notification system (Section 1.6).
- Field observation: field survey and field edits, and visible utility structures (manholes, vaults, pull boxes, valve boxes, cleanouts, markers, trench repairs, riser poles) measured and transferred to the plans.
- Geophysics: ground-penetrating radar and electromagnetic locators.
- Exposure: excavation to the utility (Section 1.2).
- Third-party and AI-assembled data: satellite imagery and AI-assembled mapping.