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Federal Highway Administration > Publications > Public Roads > Vol. 73 · No. 6 > Subsurface Utility Engineering

May/June 2010
Vol. 73 · No. 6

Publication Number: FHWA-HRT-10-004

Subsurface Utility Engineering

by C. Paul Scott

The SUE process revolutionized how designers, engineers, and contractors handle underground pipes and power lines during highway planning, design, and construction.

This technician is using an air lance to loosen soil in conjunction with a nondestructive vacuum excavation to locate an underground utility line during a project in Las Vegas, NV.
This technician is using an air lance to loosen soil in conjunction with a nondestructive vacuum excavation to locate an underground utility line during a project in Las Vegas, NV.

Every year, thousands of problems occur on highway projects in the United States when contractors fail to locate subsurface utilities reliably prior to excavation, drilling, or boring. Last year, the Common Ground Alliance, an industry association devoted to reducing damages to underground utilities, published its fifth annual Damage Information Reporting Tool (DIRT) report, CGA DIRT Analysis & Recommendations, which notes that approximately 200,000 subsurface utilities were damaged in the United States in 2008. The number is conservative because only reported hits are included.

To cite a few examples from 2008 and 2009, a Texas Department of Transportation (TxDOT) subcontractor drilled through a 20-inch (51-centimeter) water main beneath a roadway in Lubbock, TX. Repairs to the water line disrupted traffic at a major intersection for days. In a California case, a contractor excavating for a new manhole clipped an underground high-pressure line, discharging natural gas into the sky above Novato, CA, for nearly 8 hours. The leak occurred within 500 yards (457 meters) of two preschools.

This kind of problem probably happens in every State. When a Florida DOT contractor nicked a fiber-optic cable in Chipley, FL, while placing a sign during a resurfacing project, Internet service for 5,000 customers was out for 2 days. In Massachusetts, a massive outage in Braintree left about 75 percent of the city without electricity for 45 minutes after a contractor struck one of the town's primary transmission lines. These examples are only a few of many described in the January/February 2009 issue of Underground Focus magazine.

For almost 20 years, the Federal Highway Administration (FHWA) has promoted an engineering practice called subsurface utility engineering (SUE) to avoid problems like these. Before the development of SUE, traditional methods of dealing with subsurface utilities were not working. Designing projects without consideration of utilities and dealing with utility problems later during construction was common practice. This approach resulted in unexpected encounters with subsurface utilities, many unnecessary utility relocations, construction delays, and unanticipated costs.

The roadway owners in the examples described earlier probably did not locate the utilities or did not locate them correctly -- and almost certainly did not use SUE. However, largely due to extensive private-public promotional efforts, many State departments of transportation (DOTs) today use SUE routinely on Federal-aid highway and other major construction projects. As a result, they minimize the risk of costly mistakes and schedule delays, saving time and money.

"Since we began using SUE, we have been able to design around utilities and avoid utility hits during construction," says Cheryl Cathey, section chief of preliminary engineering at the Illinois DOT.

How Does SUE Work?

As an engineering practice, SUE enables State and local DOTs, design consultants, and utility companies to locate existing subsurface utilities with a high degree of accuracy and comprehensiveness. SUE combines elements of civil engineering, geophysics, and surveying. It uses surface geophysical methods (quantitative physical methods designed to interpret ambient or applied energy fields), mapping technologies such as computer-aided design and drafting (CADD) and geographic information systems (GIS), and vacuum excavation (pressurized air or water used to break up and lift soil out of the excavation area). When used properly, SUE can minimize project-utility conflicts and reduces project delays.

This SUE technician is using a pipe and cable locator and painting marks on the ground to designate the approximate horizontal position of a subsurface utility.
This SUE technician is using a pipe and cable locator and painting marks on the ground to designate the approximate horizontal position of a subsurface utility.

The SUE provider, who could be a DOT staff member but most likely is a private engineering consultant, begins by conducting extensive research of utility records to identify facilities that might affect the project under development.

The provider then obtains pertinent as-built information from utility owners and plots the resulting information on a utility composite drawing or its equivalent. The result is base-level information, termed quality level D (QL-D).

The next step involves field observations to identify visible aboveground utility features, such as manholes, valve boxes, and fire hydrants. The SUE provider surveys these observed quality level C (QL‑C) features, correlates them with the previously obtained QL-D information, and resolves any discrepancies.

Next, the SUE provider uses appropriate surface geophysical methods such as pipe and cable locators, terrain conductivity methods, metal detectors, and ground-penetrating radar to designate existing subsurface utilities or to trace a particular utility system. Weather, terrain, and utility depths, types, and materials influence the methods required, the types of equipment needed, and the cost. Several methods and types of equipment often are required for any given project. The SUE provider surveys the resulting quality level B (QL-B) information, correlates it with the QL-D and QL-C information, resolves discrepancies, and depicts it in the client's CADD system, GIS databases, or onto plan sheets or other relevant documents.

The SUE provider next develops a matrix showing all possible highway-utility conflicts. This step involves comparing the collected QL-B information on utilities with the proposed plans for the highway, bridge, drainage, maintenance-of-traffic, or other projects. One of the purposes of the conflict matrix is to determine whether additional information is needed.

Finally, the SUE provider uses minimally intrusive excavation methods, such as vacuum excavation, to expose selected subsurface utilities. Having determined the depth of the subsurface utilities and other information (size, composition, and condition of the utility, soil type, site conditions) through these targeted quality-level (QL-A) excavations, the provider then can correlate QL-A and QL-B information and depict the utility location in three-dimensions (3-D) in the client's CADD system, GIS databases, or onto plan sheets or other relevant documents.

Although these are the general steps, the practice of SUE does not follow any set pattern but rather is tailored to individual projects. Essentially, it involves systematically identifying the quality of utility information needed to design a project, then acquiring and managing that level of information.

Three SUE technicians are using a pipe and cable locator and nondestructive vacuum excavation to locate subsurface utilities. After exposing the utilities, the workers survey and record information pertinent to the type of utility and its size, depth, and condition. The workers record the data both electronically and on a poster board, which they photograph (as shown here) for quality assurance purposes.
Three SUE technicians are using a pipe and cable locator and nondestructive vacuum excavation to locate subsurface utilities. After exposing the utilities, the workers survey and record information pertinent to the type of utility and its size, depth, and condition. The workers record the data both electronically and on a poster board, which they photograph (as shown here) for quality assurance purposes.

Why Is SUE Important?

John Campbell, P.E., director of the Right of Way Division at TxDOT and chair of the American Association of State Highway and Transportation Officials' (AASHTO) Subcommittee on Right-of-Way and Utilities, initiated the SUE program in Texas. "The SUE process, specifically the assignment of quality levels to the utility data collected, provides valuable engineering information from which to make risk-based decisions...for the delivery of transportation projects," Campbell says. "At TxDOT, the use of SUE in project planning and design enables us to avoid unnecessary impacts to existing utilities and to save the incalculable costs of adjustments" that were not required because the SUE process located the utilities beforehand and construction delays never occurred.

An FHWA guidebook, Program Guide: Utility Relocation and Accommodation on Federal-Aid Highway Projects (FHWA-IF-03-014), states that the proper use of this cost-effective professional engineering service will eliminate many of the utility problems typically encountered on highway projects. According to the guide, problems reduced or eliminated include project delays caused by (1) waiting for utility relocations to be completed, so highway construction can begin; and (2) redesign when construction cannot follow the original design due to unexpected utility conflicts. Other problems avoided include (3) delays to contractors during highway construction caused by cutting, damaging, or discovering utility lines that were not known to be present; (4) claims by contractors to project owners for delays resulting from unexpected encounters with utilities; and (5) deaths, injuries, property damage, and releases of product (such as natural gas or wastewater) into the environment caused by damaging utility lines that were not known to be there.

Jeffrey Zaharewicz, FHWA value engineering/utilities program manager, describes SUE as "one of the best tools available to successfully integrate the activities associated with utility relocation and coordination into the project development process."

SUE Success Stories

A sampling of successful outcomes that resulted from the use of SUE further demonstrates the benefits of this process.

When widening I-75, the Georgia Department of Transportation (GDOT) planned to relocate existing water and sewer mains that led from a rest area to a source several miles away. After obtaining and analyzing SUE data, however, GDOT determined that no conflicts were present, and therefore relocating the lines would be unnecessary. This decision conservatively saved GDOT at least $400,000.

In Texas, the use of SUE data enabled consultants working for TxDOT to design around several high-pressure pipelines crossing a major State highway, SH-130. To achieve this outcome, the designers shifted the schematic right-of-way approximately 300 feet (91 meters), avoiding costly pipeline relocations. The right-of-way shift prevented project delays and resulted in a cost savings of $3 million.

Hurricane Wilma damaged an estimated 10,000 trees in Coral Springs, FL, that therefore needed to be removed. Wishing to be proactive and prevent costly utility damage, the city hired an SUE provider to locate utilities ahead of the tree removal crews. During the first week, SUE prevented several major utility hits. Due to the quantity of utility lines found by the provider, the city changed its approach and decided to grind many tree trunks instead of going ahead with complete stump removal. In one area, where SUE was not used, the tree removal crews hit a major water line on the first day.

Two workers are surveying a subsurface utility to determine its exact depth beneath the surface. In addition to depth, they will record on a poster board the type (gas, electric, water) and thickness of the buried utility, as well as materials, condition, and other data.
Two workers are surveying a subsurface utility to determine its exact depth beneath the surface. In addition to depth, they will record on a poster board the type (gas, electric, water) and thickness of the buried utility, as well as materials, condition, and other data.

The Early Days of SUE

The value of SUE became apparent to highway engineers when an engineering company in Manassas Park, VA, introduced the practice in 1982. The company combined two relatively new technologies -- surface geophysics and air/vacuum excavation -- to gather data on the exact location of subsurface utilities early in the development of projects.

One year later, the transportation department in nearby Fairfax County, VA, became the first government agency to use SUE on highway projects. In 1985 the Virginia Department of Transportation (VDOT) became the first State agency to use it.

"We discovered many years ago that the old ways of obtaining utilities information for design purposes were not working," says Greg Wroniewicz, VDOT utility engineer. "SUE does work, and we use it on nearly every highway project."

FHWA began promoting SUE in 1991, shortly after its nationwide potential was recognized by Jim Overton, now retired but then-acting branch chief, and Jerry Poston, now deceased but then-branch chief, of FHWA's former Railroads, Utilities, and Programs Branch. Poston was often heard to say that SUE would revolutionize the way utilities are handled on highway projects.

"His prophecy certainly came true," says Jon Obenberger, FHWA preconstruction group team leader. "Reliable subsurface utility data now can be provided to highway designers, and it is no longer acceptable practice to design highways or construct projects without consideration of those data."

How Has SUE Evolved?

By the 1990s, the new approach had spread from Virginia into nearby States (Delaware, Maryland, North Carolina, and Pennsylvania) and then to more distant States (Arizona and Florida). As the practice of SUE spread, it evolved to include surveying, CADD, affixing of a professional engineer's seal to deliverables, and professional liability insurance.

SUE flourished in the 1990s as more States began using it, and more providers began to emerge. Probably the most significant advance in that decade involved the introduction of the concept of the quality levels, which enabled designers to certify on project plans a certain level of comprehensiveness and accuracy for the utility information.

By the end of the 1990s, however, some confusion still existed as to just exactly what SUE was. Some companies were claiming that SUE meant subsurface utility exploration or "pot-holing," rather than subsurface utility engineering. The latter provides more accurate and comprehensive information than can be obtained by randomly digging pot-holes. Some DOTs bought into the former concept with poor results that soured them on continuing the use of SUE.

The leading providers were aware that SUE was an engineering practice with quality levels and were promoting it as such. FHWA also recognized the distinction between an engineering practice and pot-holing and began strongly encouraging State DOTs to acquire the services of reputable SUE providers.

The need to quantify the value of SUE on highway projects had become apparent, as well as the need to establish standard guidelines for its use. FHWA commissioned Purdue University to document and quantify SUE's value, and the American Society of Civil Engineers (ASCE), working with FHWA and industry, agreed to establish national guidelines for collecting and depicting existing subsurface utility data.

A worker loosens soil with an air lance in preparation for excavating a test hole.
A worker loosens soil with an air lance in preparation for excavating a test hole.

Research on the Effectiveness of SUE

Purdue University published its report, Cost Savings on Highway Projects Utilizing Subsurface Utility Engineering, in 2000. The Purdue researchers studied 71 projects in North Carolina, Ohio, Texas, and Virginia. The projects involved a mix of interstate, arterial, and collector roads in urban, suburban, and rural settings.

Two broad categories of savings emerged -- quantifiable and qualitative savings. The Purdue study quantified a total of $4.62 in avoided costs for every $1.00 spent on SUE. The greatest savings came from avoiding utility relocations and reducing delay claims. Although qualitative savings (for example, avoided impacts on nearby homes and businesses) were not measurable, the researchers believed those savings were significant and possibly many times more valuable than the quantifiable savings.

The study concluded that SUE is a viable technological practice that reduces project costs related to subsurface utilities and that DOTs should use it in a systematic manner.

In addition, the Ontario Sewer and Watermain Contractors Association commissioned the University of Toronto to investigate the practice of using SUE on large infrastructure projects in Ontario. This study chose nine case studies and determined that the average rate of return for each dollar spent on SUE services on those projects was $3.41. The study also made a number of qualitative recommendations regarding the use of SUE.

The ASCE Standard

In 2003, ASCE defined SUE as an engineering practice in CI/ASCE 38-02, Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data. The importance of this standard is that it indicated that, in addition to FHWA, a prominent national engineering organization defined SUE as an acceptable engineering practice and provided guidance for applying it on projects.

The standard presents the system of classifying the quality level of subsurface utility data. The classification enables project owners, engineers, and construction companies to develop strategies to reduce risks related to existing subsurface utilities or, at a minimum, to allocate the risks in a defined manner. The standard closely follows concepts already in place in the SUE profession. Many State DOTs therefore are already in compliance with the standard through their use of SUE or through their inclusion of SUE specifications in their engineering contracts.

The Private Sector And FHWA Roles

The growth of SUE resulted from efforts by FHWA's headquarters and division offices to encourage State DOTs to use it and from State DOT officials telling their counterparts about it. But some of the credit also must go to SUE professionals who understood the process and worked to sell the concept to potential clients.

FHWA encouraged the use of SUE through memos to field offices. Also, division administrators and their staff engineers discussed SUE with their State DOT counterparts and encouraged them to give it a try. FHWA developed flyers, brochures, and handbooks and distributed them to the divisions and State DOT offices; wrote numerous papers for conferences and publications; set aside funds for SUE-related research projects; delivered presentations at conferences and workshops at approximately 20 State DOTs and other venues; obtained funds to develop and/or distribute instructional videos; and funded demonstration projects in Oregon, Puerto Rico, and Wyoming.

State DOTs promoted SUE by word of mouth and continue to do so. "State DOT utility engineers get together every year to discuss common issues," says Chuck Schmidt, chief of design services at the New Hampshire DOT and vice-chair of AASHTO's Subcommittee on Right-of-Way and Utilities. "In the 1990s DOT utility engineers would meet at the National Highway Utility Conference, and for the past decade, we have gotten together at the AASHTO subcommittee conference on right-of-way and utilities. We have special sessions where we talk about our common problems and possible solutions. Those who use SUE are not bashful about singing its praises and encouraging everyone to use it. In turn, several States, including New Hampshire, have included SUE as a normal course of business on several of our projects."

While FHWA and State DOTs were promoting the new approach, the SUE professionals were on the front lines. They visited State DOTs in all parts of the country; wrote papers for conferences and articles for industry publications; provided numerous presentations, demonstrations, and exhibits at workshops and conferences; developed educational videos and provided them to FHWA for distribution; and held numerous workshops for State DOTs.

Nick Zembillas, senior principal and senior vice president, Cardno TBE, says, "Highway engineers had been locating underground utilities with inaccurate as-builts and backhoes, often with disastrous results, and it was hard to convince them that there was a better way to obtain the information. But we didn't give up and are still not giving up on the ones that continue to hold to the old ways. SUE is here to stay as an industry standard of care."

SUE Today

Federal, State, and local highway agencies are using SUE, as are design consultants, highway contractors, and utility companies for public works projects around the country. The military, airports, transit, hospitals, and ports also use it.

SUE spread from the United States into Canada in 2002 where it is used routinely on highway projects from Toronto in the east to Calgary in the west. One company alone has carried out more than 450 projects. To standardize the practice in Canada, the Canadian Standards Association is developing a standard for mapping underground utility infrastructure that will reference the use of SUE and the ASCE 38-02 quality levels.

After SUE was introduced into the United Kingdom (UK) in 2008, it slowly gained recognition in London and other major cities as a sound engineering process. Only a few small projects have been completed to date, but interest in developing something similar to the ASCE 38-02 standard seems to be growing.

An SUE technician is applying paint marks on the pavement at approximate 25-foot (7.6-meter) intervals as he traces out a utility line. After the line is surveyed, the marks will be shown on the plans as quality level B.
An SUE technician is applying paint marks on the pavement at approximate 25-foot (7.6-meter) intervals as he traces out a utility line. After the line is surveyed, the marks will be shown on the plans as quality level B.

In addition, Standards Australia is working with ASCE to develop an engineering standard similar to ASCE 38-02 in anticipation of the growth of SUE. The practice was introduced only recently in Belgium, China, New Zealand, and the United Arab Emirates.

SUE is an integral part of the National Highway Institute's course Highway/Utility Issues (FHWA-NHI-134006). The course currently is being updated to include conflict analysis, which is the newest engineering practice to evolve from SUE. SUE continues to be the subject of many presentations and workshops at conferences such as the annual conference of the AASHTO Right-of-Way and Utilities subcommittee, the Transportation Research Board annual meeting, and others.

Today, utilities should no longer be unnecessarily relocated or unexpectedly encountered on highway projects. The application of SUE by transportation agencies and qualified providers who understand the practice makes it possible to avoid utility-related problems that have plagued highway engineers for decades and thereby accelerate project delivery.

Surveyors are preparing to obtain SUE information on a project in Las Vegas, NV. The surveyed information will be depicted in the client's CADD system, in GIS databases, or on plan sheets or other relevant documents.
Surveyors are preparing to obtain SUE information on a project in Las Vegas, NV. The surveyed information will be depicted in the client's CADD system, in GIS databases, or on plan sheets or other relevant documents.

C. Paul Scott, P.E., has been Cardno TBE's national utilities liaison since 2003, joining it after retiring from FHWA, where he worked for 34 years. He received his B.S. in civil engineering from the University of Tennessee and is a registered professional engineer in Kentucky and Virginia.

For more information, please visit www.fhwa.dot.gov/programadmin/sueindex.cfm or contact C. Paul Scott at 571-233-4023 or pscott@tbegroup.com.

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