49 CFR § 195.410 - Line markers.
(1) Markers must be located at each public road crossing, at each railroad crossing, and in sufficient number along the remainder of each buried line so that its location is accurately known.
(2) The marker must state at least the following on a background of sharply contrasting color:
(i) The word “Warning,” “Caution,” or “Danger” followed by the words “Petroleum (or the name of the hazardous liquid transported) Pipeline”, or “Carbon Dioxide Pipeline,” all of which, except for markers in heavily developed urban areas, must be in letters at least 1 inch (25 millimeters) high with an approximate stroke of 1/4 inch (6.4 millimeters).
(b) Line markers are not required for buried pipelines located—
(1) Offshore or at crossings of or under waterways and other bodies of water; or
(2) In heavily developed urban areas such as downtown business centers where—
(i) The placement of markers is impractical and would not serve the purpose for which markers are intended; and
(ii) The local government maintains current substructure records.
(c) Each operator shall provide line marking at locations where the line is above ground in areas that are accessible to the public.
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