July 2018

What do those coloured lines of paint on the road and pavement actually mean?

Everyone will at some point have seen the colourful squiggly lines on the pavement, arranged as strange symbols, sometimes with letters and numbers included. They don’t usually last long and can disappear in a matter of weeks, especially if there’s been some rain. But what do they really mean, and why do they appear from time to time?

Utility Tracing Explained- 1st HorizonCongested area of service trace markings applied to the ground.

In the case of 1ST HORIZON, the lines signify buried service spray markings that have been accurately traced as part of a Utility Survey. An Underground Utility Survey involves the location of subsurface pipes, cabling and ducts within a site or area and they are usually commissioned when construction activity is planned. A variety of paint colours are used to represent the different types of underground utilities and service routes, buried below the surface.

A Utility Survey is usually carried out right at the beginning of construction planning. By mapping all subsurface conditions within a particular area, information is gathered as to where intrusive building works is safe to be undertaken. This ensures that no excavation or installation is attempted with service routes in close proximity.

Service strikes are extremely dangerous (particularly with electricity or gas services) and can result in serious injury or loss of life. As a consequence, Utility Tracing and Mapping prior to “breaking ground” is now an essential part of the modern construction process.

Damage to service routes can also be a costly matter, particularly if it results in a drop in service for the consumer. Contractors who are responsible for such damage can be subject to huge fines and penalties.

The Utility Survey process and technology used

The two primary tools used for the location of buried services are EML (Electro-Magnetic Locators and GPR (Ground Penetrating Radar). These are used to detect the services and the coloured paint markings are applied to the ground to show their accurate position and other appropriate details such as depth, size and type.

Utility Tracing Explained - 1st HorizonEML being used to locate services.

A robotic tool station is typically used, by our topographic surveyors, to accurately record the markings and trace information as well as any above ground features and detail, to produce a Topographic Survey providing background context for the Utility Survey data.

2D CAD drawings or 3D models are produced so clients can easily understand the location of buried services.

That’s what the utility traces are used for, but what do the colours themselves mean?


Yellow traces on the pavement denote gas. The amount of information sprayed in yellow depends on the nature of the subsurface gas service routes. The most common information offered along with spraying for gas pipe locations is either HP, MP or LP, meaning High Pressure, Medium Pressure or Low Pressure respectively.


As you might expect, red is associated with danger so it’s no surprise that red denotes electricity, or more specifically, service routes that carry it. Unquestionably it would be very dangerous to strike an electricity cable, and this is why it is essential to map out underground service routes before any intrusive construction process takes place. H/V means High Voltage and L/V means Low Voltage, S/L means Street Lighting.

1st Horizon GPR - Utility Tracing ExplainedGPR being used to locate services.


Blue paint is used for water supplies. If a water pipe is struck in the early construction process, you can have major problems. Earlier this year in the West Midlands an entire street was plunged under water by a ruptured watermain following a pavement excavation.


In terms of utility tracing, green paint (used for “comms” or “telecoms” cables) has become a much more popular colour over the past decade or so. There’s a simple explanation for this: broadband. In today’s world disruption to comms services can be very disruptive (particularly for businesses) so understanding their precise location when laying new services is crucial.


White is the universal colour used for comments, annotations and notes sprayed onto the pavement, white lines, or more commonly words generally accompany any colour that needs annotating to clarify meaning or to underline certain information.

Utility Survey in CAD software - Utililty Tracing ExplainedUtility / topographic survey produced in CAD software.

Are these spray paints damaging to the environment?

In short no. At 1ST HORIZON all materials used for spraying or marking surfaces for utility investigation are biodegradable, they wash away completely within a few weeks, and are safe for the environment being toluene and xylene free. They are also durable in the sense that one spray is usually enough for its intended application, making re-spraying usually unnecessary.

Utility Surveys

Utility tracing is something that we do regularly here at 1ST HORIZON. Our Utility Survey Division is active across a range of sectors, working in varied environments. We provide our clients with a best-in-class approach to understanding subsurface conditions and service route locations. You can find out more about 1ST HORIZON Utility Surveys here.

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