Reference
Chainage in road surveys: what it means and how it is referenced
Chainage is the address of a point on a road: its distance along the centre line from a fixed zero. Kilometre stones, DPR drawings and NSV files all carry it, and they need not agree. Here is what the IRC codes and MoRTH circulars say, and why the numbers part company.
Meaning
Distance along the centre line, from a fixed zero
IRC:SP:19-2001: “Distance measurements along the final centre line should be continuous following the horizontal curves where these occur.” Its drawings carry “continuous chainage”. That edition is superseded by IRC:SP:19-2020, whose text is not public.
IRC:8-1980 numbers kilometre stones from “zero at the starting station, increasing progressively upto the last kilometre stone at the terminal station”. On national highways MoRTH now sets zero State by State: “each of the States/ UTs shall have a ‘Zero’ chainage at the starting point of the NH in the particular State/ UT”. Its own example puts NH-20’s zero in Jharkhand at the Bihar–Jharkhand border near Koderma.
Within one continuous chainage, length is a subtraction. NHAI’s 2023 draft EPC agreement for the Hubli–Haveri section lists a service road from design chainage 361+300 to 361+430 as 0.130 km: 361.430 − 361.300 = 0.130.
| Point | Chainage as printed | Gap, m |
|---|---|---|
| BS2Start of transition | 401/992.971 | — |
| BC2Start of circular curve | 402/027.971 | 35.000 |
| EC2End of circular curve | 402/152.557 | 124.586 |
| ES2End of transition | 402/187.557 | 35.000 |
The curve table prints a 35.00 m transition and a 124.59 m circular arc. The chainage gaps are those lengths, round the curve, not the straight line between the points.
Notation
Plus, point or slash, and how stationing differs
Three forms appear in official documents, sometimes in the same one. We found no IRC code or MoRTH circular that prescribes one.
- PlusKm 340+000 to Km 403+400NHAI draft EPC agreement, 2023
- PointKm 0.000 to 52.100NHIDCL NSV tender, 2024
- SlashKm 402/000.000IRC:SP:19-2001 Plate 5; MoRTH’s 2019 list writes Km 486/200
SP:19-2001’s two-lane sheet uses plain metres instead: “CH.2950.00 to 4100.00”. The NHAI agreement also lists land widths at chainage 360.500, 360.550 and on.
In Hindi. The Gazette of India transliterates it. A 2024 notification heads its column “चैनेज” and writes “किमी 43.30 से किमी 91.00 तक”.
Stationing is the US form of the same idea, counted in feet. North Dakota DOT’s survey manual: “Stationing will increase continuously from the beginning of a highway. Station 0+00 will begin at the zero (0) reference point.” Its plus sits “between the second and the third digit left of the decimal point”, so a station counts hundreds of feet. In Indian chainage the plus separates kilometres from metres, as the service road above shows.
On the road
Kilometre stones and 200 m stones
IRC:8-1980 and IRC:26-1967 are the current editions on IRC’s list of 28 September 2026, and MoRTH’s 2019 procedure names both for national highways.
- Two sizes
- National highways, state highways and major district roads carry “ordinary kilometre stones” and larger “fifth kilometre stones”, “installed after every five kilometres” (IRC:8-1980 cl. 2.2).
- Which side
- “Normally kilometre stones shall be located on left-hand side of the road as one proceeds from the station from which the kilometre count starts.” Divided roads get them “at the left on both sides of the road i.e. independently for each direction of travel” (cl. 7.1). MoRTH’s 2019 procedure repeats this.
- Colour
- The semicircular top is canary yellow on national highways, brilliant green on state highways and white on major district roads (cl. 6.1).
- 200 m stones
- On the same side as the kilometre stones, numbered “2, 4, 6 and 8 … in an ascending order in the direction of increasing kilometrage away from the starting station” (IRC:26-1967 cl. 3–4). IRC:SP:84-2019 puts them “at every 200 m distance” on four-lane highways.
- Not always there
- The numbering “is meant for the use of maintenance staff” (IRC:8). MoRTH recorded in 2016 that “In case of some of the National Highways Km stones are missing”, and in 2019 that in most cases the stones and marking were “still being done as per Old NH nos.”
Why they disagree
One point, three chainages
A point can carry the number on the nearest kilometre stone, a design chainage, and a distance summed from GPS. The documents show four reasons they differ. Each example below is a single printed case, not a typical difference: we found no source that measures one.
1. Realignment changes length
In 1987 MoRTH wrote of “change in the overall length because of construction of new byepasses, realignment of existing roads and/or geometric improvements”, and chose not to renumber. Continuous renumbering followed in 2003; by 2006 MoRTH noted that “The documents and records at present may have different chainages than the chainges [sic] with new re-numbered kilometer stones.” Since 2019, a bypass that is built, under construction or tendered joins the chainage “in continuity”; one at DPR stage changes nothing.
2. Renumbering leaves two kilometrages
MoRTH’s 2019 list describes a stretch of NH-44 in Hyderabad “from Bowenpally [Km 486/200](old Km 474/00) to Assembly [497/200](Old km 485/0)”: the same points, 12.2 km apart in the two numberings. In 2024 the Gazette restated the end of an NH-87 section as Km. 91.00 instead of Km. 88.00, giving no reason.
3. Existing and design chainage are separate references
SP:19-2001’s four-lane sheet draws the existing stone, “EX. Km 402/000.000”, at design chainage 402/072.000: 72 m from the design’s own km 402. It is an illustration in a manual, not a measured offset.
4. GPS distance is not chainage
California’s highway department: “The use of latitude and longitude cannot directly calculate the distance along the roadway between two locations.” Summed GPS fixes are biased too: at high sampling rates “the distance between two points recorded with a GPS is – on average – bigger than the true distance” (Ranacher et al., 2016), while sparse fixes cut corners and can come out short. NHAI’s survey vehicles carry a separate “DMI (Distance Measuring Indicator)” beside DGPS.
How an NSV format ties them together. NHIDCL’s 2024 NSV output format keeps a “Location Reference Post (LRP) Master”: each kilometre stone, such as “Km stone 17”, with its own chainage, direction, latitude and longitude. In its sample table Km Stone 17 sits at 17.085.
In the deliverables
What MoRTH asks you to reference
MoRTH circular 130.265 (2 September 2026) adds a data-products table to the standard DPR RFP. Chainage and coordinates run through it.
The 2025 terms of reference record inventory “@ every 500m and every change of feature whichever is earlier”, and require that “All defects shall be systematically referenced, recorded and quantified”.
With every chainage, name its reference (existing stones, design alignment or GPS distance) and carry latitude and longitude beside it. The 2026 format asks for coordinates throughout, and for both existing and design chainage at cross sections; naming the reference is our advice, so that records made against different references are not mixed.
| Row | Data product | Contents required |
|---|---|---|
| 2.7 | Longitudinal and cross sections | “Location of cross section - existing, design chainage, lat, long, Cross section drawing” |
| 2.12 | Pavement investigation | “Test pit reference id, location, chainage, geo-reference (lat, long) …” |
| 2.13 | Pavement condition survey | “Data as required in clause 4.11.3.2, along with location/chainage and geo-reference for all data” |
| 2.11 | Road inventory surveys | “All data as required in clause 4.11.3.1, geo-referencing for each row of data in lat, long form” |
| 1.1 | List of traffic survey points | “Point no, location coordinates (lat, long), location of survey point, chainage …” |
| 2.4 | Video | “Traverse video of entire project length” |
Row 2.4 sets a file format for the traverse video, .avi or .mp4, and nothing about how it is referenced to chainage.
Where Playcraft fits
Chainage on every frame, and what it is not
Playcraft Chainage is an Android app for a phone in a car mount. It burns chainage, GPS, speed, heading, tilt and time into the video as it records.
Its chainage is cumulative GPS distance from where the recording starts, with the bias above. Chainage along a design alignment you supply, with the snapping caveats Caltrans lists at junctions and on winding roads, is something we build on demand. The position stream passes accuracy gating, jump rejection and a Kalman estimator, holds still when speed stays below about 1 km/h for 3 s, and is kept with the chainage series as CSV and JSON.
What it is not: its chainage is not survey-grade position, and we publish no chainage-accuracy figure. Its roughness estimate is not a certified roughness instrument of any class, nor a figure to accept or reject a contract against; see road roughness as per IRC.
Built on demand, not shipped: a chainage-referenced video portal (scrub to a chainage and see the frame there), and a road asset inventory that includes kilometre stones. We build these on demand. See also the NSV survey.
Sources
- IRC:8-1980, Type Designs for Highway Kilometre Stones (Second Revision)Indian Roads Congress · cl. 2.2, 4.6 and footnote, 6.1, 7.1 · 1980, reprinted 2012
- IRC:26-1967, Type Design for 200-Metre StonesIndian Roads Congress · cl. 3, 4 · November 1967, reprinted 2016
- IRC:SP:84-2019, Manual of Specifications and Standards for Four Laning of Highways (Second Revision)Indian Roads Congress · cl. 12.3(b) · August 2019
- IRC:SP:19-2001, Manual for Survey, Investigation and Preparation of Road ProjectsIndian Roads Congress · cl. 12.2.5, 17.4.3; Plates 2 and 5; superseded by the 2020 edition, not public · 2001
- Standard Operating Procedure for installation of kilometer stone as per rationalization in the numbering system of NHs (603.18)MoRTH · OM NH-15017/33/2019-P&M, para 2, 3.4, 4.1; Annexure-B · 16 August 2019
- Re-numbering and refixing of kilometre stones on National Highways (603.10)MoRTH · RW/NHIII/P/24/76 Vol. III · 28 January 1987
- Procedure for numbering of kilometre stones on National Highways (603.11)MoRTH · RW/NH-33044/10/2002-S&R(R) · 11 February 2003
- Numbering of kilometer stones on National Highways (603.16)MoRTH · RW/NH-33044/27/2004-S&R (R) · 28 June 2006
- Setting up and numbering kilometer stones as per the new NH numbering scheme (603.17)MoRTH · RW/NH-33044/149/2016/S&R (R) · 25 October 2016
- Notification S.O. 3462(E), amending S.O. 452(E)MoRTH (Gazette of India) · NH-87 (new NH-9, 109), Uttarakhand · 14 August 2024
- Revised RFP for consultancy services for preparation of Detailed Project ReportsMoRTH · Circular 130.247, Terms of Reference cl. 4.11.3.1, 4.11.3.2 · 29 September 2025
- Revised RFP for DPR consultancy — amendment (circular 130.265)MoRTH · Enclosure-IV, Data products · 2 September 2026
- EOI for NSV survey of NH-10 Sevoke–Rangpo, Annexure I “Output format from Network Survey Vehicle”NHIDCL · NHIDCL/PMU-Siliguri/Survey/2024 · 4 December 2024
- NHAI to deploy Network Survey Vehicles across the country for over 20,000 km of National HighwaysNHAI · Press release · 22 October 2025
- Draft EPC agreement, six-laning of km 340+000 to km 403+400, Hubli–Haveri section of NH-48NHAI · Schedule-A, Annex-I · June 2023
- Surveys & Photogrammetry Manual, Chapter 18: Field Data Collection for 90-1 SurveysNorth Dakota DOT (US practice) · p. 18-3 to 18-4 · revised 14 April 2026
- DGP-04, Linear ReferencingCaltrans (US practice) · Background; Latitude and Longitude · 9 May 2023
- Ranacher et al., Why GPS makes distances bigger than they areInternational Journal of Geographical Information Science · 30(2): 316–333 · 2016
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