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.