Decode colored lines which mark utilities underground

Subterranean infrastructure and utility lines are marked using a color coordinated system which allows contractors and locators to easily identify what lies beneath. This handy guide aims to explain what these colors mean and where they came from.


This system was first developed and deployed in California after a fatal accident (2) in the petroleum industry, but would go on to evolve and incorporate more colors and utilities.

The American Public Works Association went on to establish a standard color code to identify subterranean infrastructure in American cities. These safety colors expanded to include red, orange, yellow, green, blue, purple, brown, grey, white, and black and now denoted as Safety Color Code Z535 (3) by the American Standards Institute (ANSI).

In addition to colors the lines themselves are also significant. The Guidelines for Operator Facility Field Delineation established by the CGA states that, spray-painted lines which are spaced between four and fifty feet apart should be used to mark the center of a single facility. However if multiple conduits are in a single trench, two parallel lines with a PERPENDICULAR one in the middle (like an H) (4) are marked down with an arrow denoting the direction services are going.

If there is a duct system in place a diamond is used instead of the perpindicular line. The width of these marking should reflect the approximate width of the trench if known. Unfortunately these markings aren’t always enough to mitigate damages.


We’ve designed Utilocate to be compliant with these colors and markings, making it easier for locators to mark on their drawings where utilities are positioned. Damage prevention is only possible when we use the all the tools at our disposal and work collectively and so we want to make it easier for locators to denote digitally what lies where. Markings on the ground are not a perfect solution, because they can be washed away, painted over or messed with. Digital drawings with accurate markings improve safety, reduce damages and are viewable not only in the field but also in the office.

If you’d like to learn more about digital drawings within Utilocate then please reach out to us at or phone +1 877-395-1122

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