Utility location is the process of identifying and labeling public utility mains which are underground. These mains may include lines for telephones, electricity distribution, natural gas, cable television, fiber optics, traffic lights, street lights, storm drains, water mains, and wastewater pipes. In some locations, major oil and gas pipelines, national defense communication lines, mass transit, rail and road tunnels also compete for space underground.
Public utility systems are often run underground; some by the very nature of their function, others for convenience or aesthetics. Before digging, local governments often require that the underground systems' locations be denoted and approved, if it is to be in the public right-of-way.
Because of the many different types of materials that go into manufacturing each of the different types of underground lines, different detection and location methods must be used. For metal pipes and cables, this is often done with electromagnetic equipment consisting of a transmitter and a receiver. For other types of pipe, such as plastic or concrete, other types of radiolocation or modern ground-penetrating radar must be used. Location by these technical means is necessary because maps often lack the pinpoint precision needed to ensure proper clearance. In older cities, it is especially a problem since maps may be very inaccurate, or may be missing entirely.
A few utilities are permanently marked with short posts or bollards, mainly for lines carrying petroleum products. This may be done because of venting requirements, and also serves to indicate the location of underground facilities that are especially hazardous if disturbed.
"Call before you dig", "Digger's Hotline", "One-call", "Miss Utility", "Dig Safe", or Underground Service Alert are services that allow construction workers to contact utility companies, who will then denote where underground utilities are located via color-coded markings at those locations. As required by law and assigned by the US Federal Communications Commission (FCC), the 8-1-1 telephone number is used for this purpose across the United States.
Failure to call such a number ahead of time may result in a fine or even a criminal charge against a person or company, particularly if such negligence causes a major utility outage or serious accident, or an evacuation due to a gas leak. Hitting a water main may also trigger local flooding or require a boil-water advisory.
Utility color codes are used to identify existing underground utilities in construction areas, to protect them from damage during excavation. Colored lines, flags, or both are used to mark the location and denote the type of underground utility. A special type of spray paint, which works when the can is upside-down, is used to mark lines, often in a fluorescent color. On flags, a logo often identifies the company or municipal utility which the lines belong to.
Flags may also be an advertisement for a company which has installed an irrigation system for lawns or gardens. In this case, each sprinkler head is usually marked, so that landscaping crews will not cover or bury them with soil or sod, or damage them with tractors or other construction equipment while digging holes for trees, shrubs, or other large plants or fenceposts. This is also important because a vehicle (tractor, truck, or otherwise) can break a sprinkler or the hard-PVC pipe or joint it is mounted on, simply by driving over it, particularly on newly moved soil which is uncompacted and therefore unsupportive of such weight.
The American Public Works Association (APWA) Uniform Color Codes for temporary marking of underground utilities are listed below:
|Red||electric power lines, cables, conduit, and lighting cables|
|Orange||telecommunication, alarm or signal lines, cables, or conduit|
|Yellow||natural gas, oil, steam, petroleum, or other gaseous or flammable material|
|Green||sewers and drain lines|
|Purple||reclaimed water, irrigation, and slurry lines|
|Pink||temporary survey markings, unknown/unidentified facilities|
|White||proposed excavation limits or route|
The United Kingdom uses a convention very similar to the US one, for marking underground utilities, such as telephone, gas, water and electricity. These markings are by convention colour-coded, and are painted by contractors onto the pavement.
Example utility maps and markings
- DigNet, coordinators of digging activities
- Ditch Witch, manufacturer of horizontal drilling equipment
- Dynatel, a product line of utility locators and markers
- Underground Service Alert
- "USDA Utilities". USDA. Retrieved October 5, 2013.
- "811. Know what's below. Call before you dig". call811.com. Common Ground Alliance. Retrieved 2013-07-24.
- Cawley, Laurence. "What do those squiggles on the pavement actually mean?". BBC News. Retrieved 19 February 2014.
- Technology Transfer Information Center. "Statement of Need: Utility Locating Technologies". Accessed October 31, 2007.
- Common Ground Alliance, a member-driven association promoting safety and damage prevention practices to underground facilities in North America
- American Public Works Association, an organization of public works professionals
- National Utility Locating Contractors Association, a utility locating organization