If you work on Queensland's state-controlled roads, you'll hear "chainage" every day: on traffic guidance schemes, permit applications, work orders, defect lists and over the radio. It's simply a way of saying exactly where something is along a road. This guide explains what it means, where it comes from and how the Department of Transport and Main Roads (TMR) system works, in plain English.
Chainage in one sentence
Chainage is the distance along a road, measured from a fixed starting point. If a pothole is at chainage 25.306 km, it's 25 kilometres and 306 metres along the road from where that road's measurement starts.
That's it. Everything else in this guide is about the details that make the number useful: which road, which starting point, which direction and which side.
Where the word comes from
Before tape measures and GPS, surveyors measured land and roads with a chain. The most famous, Gunter's chain, was devised by the English mathematician Edmund Gunter in about 1620. It was 66 feet long (about 20.1 m) and made of 100 links. A distance measured by laying the chain end to end along a line was its "chainage".
The chains are long gone, but the word stuck. Today chainage is measured in metres and kilometres, from digital road centrelines, with survey equipment and GPS.
How TMR measures chainage
Queensland's state-controlled road network is about 33,460 km of motorways, highways and major roads managed by TMR. To give every point on it an address, TMR breaks each road into road sections and measures distance along each one.
Road sections
Each state-controlled road has a number, and long roads are split into sections with a letter suffix. The Bruce Highway is road 10, split into 14 sections from 10A (Brisbane–Gympie) to 10P (Innisfail–Cairns). TMR allocates section codes in order along the road, so 10A comes first, then 10B, 10C and so on. Some other roads have a single section with a plain number, and urban arterials have their own codes, such as U14 for Gympie Arterial Road.
Through distance
TMR's open data calls chainage through distance: "the distance in kilometres measured from the gazetted start point of the road section". It starts at 0 at the beginning of every section. So the Bruce Highway doesn't have one chainage from Brisbane to Cairns; it has 14, one for each section, each starting again at zero.
That's why a chainage on its own is meaningless. "Chainage 25.3" could be on any of hundreds of road sections. You always need the road section with it.
Gazettal direction
Every road section has an official direction, called the gazettal direction: "the officially declared direction of a road with a start point and an end point". For section 10A it's Brisbane to Gympie, so chainage increases as you head north. Travelling the other way is the anti-gazettal (or against-gazettal) direction, and chainage counts down.
Carriageways: which side of the road?
A two-lane country highway has one carriageway. A motorway has two, one each way, plus ramps, service roads and sometimes busways. TMR gives each its own carriageway code so a chainage can point to the right one:
| Code | Meaning |
|---|---|
| 1 | Primary through carriageway, undivided (a normal two-way road) |
| 2 | Primary through carriageway, divided, in the gazettal direction |
| 3 | Primary through carriageway, divided, against the gazettal direction |
| 4 and 5 | Outer primary carriageways on wider divided roads |
| A to E, Q to U | Other carriageways to the left (A–E) or right (Q–U) of the primary, such as ramps and service roads |
| K to P | Carriageways between the two sides of a divided road |
| V, W / X, Y | Roundabout connections / flyover and underpass carriageways |
Section 10A, for example, is divided all the way from Brisbane to Gympie, so it has carriageways 2 (northbound) and 3 (southbound) for its full length, plus a long list of ramps and service roads. On a divided road, saying "carriageway 2" or "northbound" with your chainage removes any doubt about which side you mean.
How to read and write a chainage
TMR's drafting standards abbreviate chainage as Ch and give it to three decimal places of a kilometre, which is to the metre. You'll see the same location written several ways:
- Ch 25.306 km or 25.306 km: kilometres to three decimal places, as in TMR's data and reports.
- Ch 25+306: the engineering "kilometres plus metres" form, common on design drawings and in the field.
- 25306 m: plain metres, sometimes used in spreadsheets.
All three mean the same point. A complete reference adds the road and section, and the carriageway where it matters:
Bruce Highway, section 10A, carriageway 2, Ch 25.306 km
For a stretch of road, such as a work zone or a lane closure, give the start and end chainage: "10A Ch 25.300 to 25.900 km".
Where you'll come across it
- Traffic management: traffic management plans and traffic guidance schemes locate the works, and the national guide for field staff lists chainage among the ways to locate the work area on site. See chainage in traffic guidance schemes.
- Permits: TMR's traffic control permit form asks for the start and end location as a cross street or chainage. See road corridor permits vs traffic control permits.
- Design and survey: TMR's surveying standards say the road number, name, section and gazettal distance form the chainage datum for a project.
- Maintenance and asset management: defects, signs, culverts, guardrail and other assets are recorded against road section and chainage.
- Traffic data: TMR publishes traffic counts (AADT) by road section and through distance.
Why chainage can change, and why markers can disagree
Chainage is tied to the road's centreline, and centrelines change. When a road is realigned (a bypass, a straightened curve, a new interchange), the length of the section changes, and chainages further along can shift. TMR updates its data to reflect new road projects, but the update can lag behind the construction.
Through distance has traditionally been measured by driving the road with a precise distance-measuring instrument, and TMR describes it as accurate to about 10 m. Roadside distance plates and older drawings may use a different datum or date. So a chainage from a 15-year-old drawing, a roadside marker and today's TMR data can differ by a few metres, or more after a realignment. When it matters, check which data a chainage came from.
Finding a chainage quickly
You can look chainages up in TMR's open data, the Queensland Globe mapping service (which can show 1 km marks along state-controlled roads) or GIS software. In the field, the fastest way is an app that does the lookup for you.
Chainage gives you the road, section, carriageway and chainage for any point on a Queensland state-controlled road: tap the map, use your phone's GPS, or paste coordinates or a Google Maps link. It works in the browser on any phone, and finding chainages is free. See how to find the chainage of where you're standing.
Frequently asked questions
What does chainage mean on a road?
Chainage is the distance along a road from a fixed starting point. On Queensland's state-controlled roads it's measured in kilometres from the start of each TMR road section, in the gazettal direction.
What is through distance?
Through distance is TMR's name for chainage in its road data: the distance in kilometres from the gazetted start point of a road section. It starts at zero at the beginning of every section.
What does Ch 12+345 mean?
It means chainage 12 kilometres plus 345 metres, the same as 12.345 km. The plus form is common on design drawings; TMR's data uses kilometres to three decimal places.
What is gazettal direction?
The officially declared direction of a road section, from its start point to its end point, for example Brisbane to Gympie for Bruce Highway section 10A. Chainage increases in the gazettal direction.
Do council roads have chainage?
Councils may use chainage on their own drawings and asset systems, but TMR road sections and through distances only cover state-controlled roads. To check who manages a road, see our guide to state-controlled and council roads.
Why is it called chainage?
Surveyors once measured distances with a chain. Gunter's chain, devised around 1620, was 66 feet long with 100 links, and a distance measured with it was its chainage. The name outlived the chain.
Sources
- Queensland Department of Transport and Main Roads, Road Location and Traffic Data definitions, including the carriageway code table.
- Queensland Government Open Data Portal, Road location and traffic data and its fact sheet.
- TMR, Surveying Standards Part 1, chainage datum and gazettal chainage.
- TMR, Drafting and Design Presentation Standards, Volume 1, Chapter 2, chainage abbreviation and precision.
- TMR Annual Report 2025–26, state-controlled road network length.
- Science Museum Group, Gunter-type measuring chain.
- Austroads, Guide to Temporary Traffic Management Part 6: Field Staff.