Beneath our households, sidewalks, and backyards, a hidden network of utilities enables a multitude of services to be delivered to consumers, like roots to a tree. Across the U.S., there are more than 20 million miles of underground utility infrastructure. These range from municipal sewer lines to privately-owned telecommunications lines to natural gas distribution pipelines. When a One-Call center is contacted, locators may mark up to five or size different utilities using color-coded flags or spray paint.

A single site can have multiple pipes, cables, and wires depending on the surrounding environment being urbanized or largely rural. A farm may have a long transmission pipeline buried under its land, while a suburban home is likely attached to the energy grid through subterranean power lines, while a host of water, gas, sewage, and other pipes connect to private and municipal utilities.

These are all revealed when an excavator plans to dig and calls 811. The spray paint identifies the type of utility.

White spray paint or flags are used to demarcate the location of a proposed excavation to give locators a better idea of where digging will occur so they can be particularly certain to mark utilities in that area. White is used by the excavator before calling 811 in the first place.

The color red identifies underground electrical power lines, cables, and lighting conduits. Yellow is reserved for more dangerous utilities like gas, oil, steam, or petroleum lines that could pose a substantial risk if ruptured. These utilities would be the most important to locate due to the volatility of resources that are transported and potential impact to the wider community if disrupted.

Municipal services like water and sewer lines must also be accounted for in an urbanized setting. The color blue is used to mark potable water lines, while green is used to show the location of underground sewer and drainage lines. Finally, the color purple shows reclaimed water, irrigation, or slurry lines that are underground.

Average suburban households contain at a minimum: water, sewage, gas, and telecoms. On average, a single locate request results in five to six utility companies responding. Dig sites in urban areas will have to contend with multiple utilities serving both the surrounding buildings and the city-wide utilities like sewer systems.

Overall, the more densely populated an area is, the higher the potential for multiple utilities to be extremely close together. Knowing which color corresponds to a specific utility can prevent damage to the Modern Roots.


Learn more about Aii’s #ModernRootsMarch by visiting its webpage here.


Written by Roy Mathews, Public Policy Associate


The Alliance for Innovation and Infrastructure (Aii) is an independent, national research and educational organization. An innovative think tank, Aii explores the intersection of economics, law, and public policy in the areas of climate, damage prevention, energy, infrastructure, innovation, technology, and transportation.