Virginia DOT is using tiny computer chips inside buried plastic spheres to store the location, ownership, attributes, placement date, orientation, depth, and assets buried nearby with public and private utilities via a master geodatabase. Photo: 3M
Virginia DOT is using tiny computer chips inside buried plastic spheres to store the location, ownership, attributes, placement date, orientation, depth, and assets buried nearby with public and private utilities via a master geodatabase. Photo: 3M

Like any highway engineer, Matt McLaughlin dreads coming across unexpected water, gas, cable, sewer, and electrical lines.

“It costs more than $1,000/hour to put an excavator on hold while a buried utility question is resolved,” says McLaughlin, who oversees construction of the relocated utilities related to roadway construction in the Northern Virginia District for the Virginia State DOT (VDOT). “And in the case of a damage incident, the safety implications, in addition to public safety costs, are even greater — not to mention the cost of the repair, possible evacuations, and personal injury or loss of life.”

In his quest to minimize these challenges on a $70 million reconstruction project in suburban Washington, D.C., McLaughlin made VDOT the first state transportation department to implement electronic marking intended for use by all participating utilities. The system combines radio-frequency identification (RFID), GPS, and GIS technologies, and is being developed by VDOT; the Gas Technologies Institute; the Virginia Utility Protection Service, which is the state one-call operation center; and others to create a single repository for buried utility mapping to which all stakeholders contribute and refer.

It's being tested at an intersection where two major routes, each with four lanes, are being expanded to six lanes with 28-foot medians. The average distance between pipe crossings along the 60-foot-wide roads is 3 feet, and more crossings will be added during the three-year utility-relocation phase. The crossings must be free of grade cuts, drainage crossings, traffic signals, and other construction elements.

“The relocation work is substantial, with every utility interest represented, including gas, telephone, power, CATV, two water authorities, sanitary sewer, and 13 fiber-optic companies, so the accuracy of the relocated facilities will have a significant impact to the project,” says McLaughlin.

Passive underground markers have been in use for more than three decades, but RFID markers have capitalized on the signal transmitted by an interrogating device — in this case, a handheld RFID tag locator — and are designed to last for the life of the buried asset. Power is provided by the signal from the interrogating device signal, and information is read as a reflective radio frequency response.

Accuracy is another benefit. It helps eliminate the interference and false marking common to standard locators, particularly in areas as congested as McLaughlin's project site.

Although GPS is an important component of asset management for utilities and road departments, it provides only submeter accuracy, not the accuracy needed in real-world environments. An RFID tag identifies an asset within inches.

Likewise, conventional tracking provides only approximate position and depth; and when there are high-voltage lines overhead, a high water table, or other pipes or metal objects in close proximity, it can be difficult to pinpoint and accurately identify specific buried assets. Radio waves can distinguish not only between utilities but also between the specific assets of a particular utility when adjacent markers are tuned to the same frequency. This information is conveyed by the data programmed into the RFID tag.

What McLaughlin needed was a primary physical marking and locating method that would deliver accurate and reliable point location despite soil conditions, nearby utilities, or the temperature extremes normally found underground. He also needed a system that would translate his department's GPS language — station numbers and offsets — into the GPS language of latitude and longitude coordinates that utilities use.

His contacts at the Virginia Utility Protection Service told him about a programmable electronic marking system that 3M Track and Trace Solutions introduced in 2002. The system is composed of a waterproof device — the 3M EMS 1400 Series iD ball marker — that houses an RFID chip that can be found easily from above-ground using the portable Dynatel 2200M Series ID marker locator.

Buried next to an underground asset, the marker's antenna transmits its location as a reflective radio frequency response to the locator along with the marker's unique identification number, information about who owns the asset, the asset's function (splice, valve, service tee, direction change), and its depth.

McLaughlin's team decided that about 600 marker balls would be needed to identify the relocated utilities at a cost of $15/marker — or about $10,000 total including installation.

Then McLaughlin developed a master utility relocation plan that includes entering marker data immediately into a master GIS database to be delivered to participating utilities. So although each party owns the data on its assets, it can share the information with other stakeholders via a single-point repository that's still being developed and will be password-protected for security. The Virginia Underground Protection System will host the combined database.

According to agreed-upon protocol, utilities must install markers on relocated assets every 50 feet for metallic pipes and every 25 feet for nonmetallic pipes; at points of horizontal and vertical direction change; at critical utility crossings; appurtenances that are important to the utility; service connections; and abandoned facilities. To quickly locate service connections, the facility's address and other specific data can be programmed into the RFID tag to enhance accuracy.

Using a template provided by 3M, McLaughlin's construction managers or inspectors enter the data for each utility's assets — a unique 10-digit serial number, as well as the name of utility owner, item description (gas, water, or cable TV), item details (valve; splice; service tap; horizontal and vertical change in direction), placement date, depth below grade, orientation, elevation, and information about adjacent items (for example, that a pipe or cable lies below) — into the master database. Each utility owns the data it collects.

The department developed a compressed code for this purpose that fits within the available 256-bit RFID tag's memory capacity and is useful across utility categories. Construction managers also worked with 3M to modify templates to maximize the amount of information that can be programmed into the tag.

“Our pilot program confirmed the usefulness of these markers to improve both the accuracy and efficiency of locating underground utilities and minimized the potential for costly damage,” McLaughlin says. “This is a ‘safety first' initiative.”

— North is a product manager for 3M Track and Trace Solutions in Austin, Texas.

How it works

As contractors reinstall pipes and cables, they give Matt McLaughlin, who oversees the construction of the relocated utilities related to roadway construction in the Northern Virginia District for the Virginia State DOT, and his crew the elevations for where the markers will be installed. Inspectors add that information to each marker's file and transmit all the information about that marker via the portable locator.

Once programmed, the 4-inch plastic spheres are dropped into the backfill material of the trench at a selected, pre-recorded depth (generally 3 to 4 feet below grade), taking future grade changes into account. The spheres are distinguished by colors and interrogation frequencies for each of the seven utilities. After backfilling, the department takes GPS readings at each site to include the marker coordinates in addition to the rest of the data stored on each marker in the master GIS database.

Programming and marker placement can be done without delaying excavation or utility placement. Daily data entry means that mapping details are regularly updated and quickly accessible to stakeholders. The distributed record consists of a PDF file with all GIS data, including pop-ups f for each marker position that list programmed data and GPS coordinates. Utility employees can view the information on a computer screen merely by placing the cursor at a specific location.

McLaughlin expects the database to enhance the partnership between his agency, utilities, the Virginia Utility Protection Service, and the Virginia State Corporation Commission. The system is now being applied to an interchange project in Gainesville, Va., as well as other smaller projects in Northern Virginia.