TMH 13 explained: seven parts of automated road condition assessment

TMH 13 is the South African road manual that describes how to plan, run and check automated road condition assessments, and it has seven parts, A to G, not one parameter. TMH (Technical Methods for Highways) is a series of South African road manuals compiled under COTO, the Committee of Transport Officials (COTO, 2016d). TMH 13 (Committee Draft Final, May 2016) covers positioning, roughness, rutting, skid resistance and texture, surface deflection and imaging (COTO, 2016d).

Key facts

• TMH 13, Automated Road Condition Assessments, is a South African road manual in seven parts, A to G, compiled under COTO, the Committee of Transport Officials.
• TMH 13 has seven parts: A is general concepts and planning, B positioning, C roughness, D rutting, E skid resistance and texture, F surface deflection and G imaging.
• TMH 13 Parts C, E, F and G classify their devices or systems and Parts B and D define no classes, so quote a class number with its part letter.
• TMH 13 Parts B to G share one layout of measurement devices; calibration, validation and control testing; and operational and quality control procedures.
• TMH 13 describes how to measure road condition, TMH 22 Part D (road asset management) lists what a road authority collects, and TMH 18 lists file formats for submitting results.
• TMH 13 is a Committee Draft Final dated May 2016 with no legal standing, so a survey contract should name the edition and the acceptance criteria.

What are the seven parts of TMH 13?

Automated road condition assessment means measuring a road with vehicle-mounted instruments rather than by eye, mostly at traffic speed. TMH 13 divides that work into seven parts and is a companion to TMH 22 (Draft, March 2013), the road asset management manual (COTO, 2016d).

• Part A, General. Sets out the measurement concepts and how to plan a network condition survey (COTO, 2016d).
• Part B, Positioning. Describes GPS (global positioning system) receivers, inertial sensors and the distance measuring instrument (DMI), and how to validate them (COTO, 2016c).
• Part C, Roughness. Describes how roughness is measured, classified and checked, including the International Roughness Index (IRI), a roughness statistic computed from the measured longitudinal profile and reported in metres per kilometre (COTO, 2016a).
• Part D, Rutting. Describes measuring rut depth, the depth of the depression in a wheelpath (the strip of lane a wheel follows), with reference devices and high-speed profilers (COTO, 2016e).
• Part E, Skid Resistance and Texture. Describes the devices that measure skid resistance and surface texture, and how the two are related (COTO, 2016f).
• Part F, Surface Deflection. Describes deflectometers, including the falling weight deflectometer (FWD), and the strength parameters derived from a deflection bowl (COTO, 2016g).
• Part G, Imaging. Describes imaging systems from frame imaging to three-dimensional (3D) laser scanning, and how to validate them (COTO, 2016h).

Cite the part letter every time: "TMH 13 Part C" names roughness, whereas "TMH 13" alone does not say which measurement is meant.

Which TMH 13 part answers which question?

Each TMH 13 part answers its own question and leaves its own record, and the table adds where that record lands in TMH 18 (Road Asset Data Electronic Exchange Formats, Draft Version 4, October 2014). A .cid file is the Combined Instrument Data file, and a .fwd file holds normalised deflection bowls (COTO, 2014).

Part	Question it answers	Record it produces	Where it lands
A	How is the survey planned and proved?	Specification, validation sections, reports	The contract
B	Where on the road is each reading?	Position and distance for every record	Km and coordinate fields
C	How rough is the ride?	IRI for each wheelpath	.cid file
D	How deep are the ruts?	Average rut depth for each wheelpath	.cid file
E	How much texture and grip?	Mean profile depth (MPD), skid resistance	MPD in .cid file; no skid file
F	How does the structure deflect?	Bowls, load, temperatures	.fwd file
G	What does the surface look like?	Images with location references	No image file type

TMH 18 Committee Draft 5.0 (February 2016) keeps the .cid file, and its file-extension table lists raw FWD data in the F25 format under .fwd (COTO, 2016i). The reference page on texture and skid explains why those two records differ, and the comparison of IRI, rut depth and texture depth separates the three .cid measurements.

Narrated film · 1:28

TMH 13: the seven parts

A seven-part fan opens from the title, positioning slides underneath Parts C to G, and each part is tagged with the record it produces.

Read the film transcript

Ask for TMH 13 in a survey specification, and the first question back should be: which part? TMH 13 is a South African road manual, compiled under COTO, the Committee of Transport Officials, on measuring roads with vehicle-mounted instruments. There are seven parts: Part A covers planning, and Parts B to G cover positioning, roughness, rutting, skid resistance and texture, surface deflection and imaging. Part B sits underneath the rest, because a reading is useful only once it is placed on the road. Each measurement part leaves a record: the International Roughness Index, rut depth, mean profile depth, skid resistance, deflection bowls, and images with locations. Parts C, E, F and G classify their devices; B and D define none, so quote a class with its part letter. As a Committee Draft Final of May 2016, TMH 13 has no legal standing, so cite the edition. It is not a complete specification, and it does not select a treatment. Part F is titled Surface Deflection; where TMH 13 says TMH 20 for data formats, it points to TMH 18. TMH 22 Part D lists what a road authority collects. TMH 13 describes how each is planned, run and checked. TMH 18 lists the file formats for the results. Cite the part letter every time, because TMH 13 never means one parameter. Next, read TMH 22 Part D, then TMH 18, naming its version.

Which TMH 13 parts define device classes?

In TMH 13, Parts C, E, F and G each classify their devices or systems; Parts B and D define none. In Part C the roughness measurement classes (section C.2.1, Table C.1) run from Class 1 precision profiles and Class 2 non-precision profiles to Class 3 IRI estimates from calibrated response-type devices (COTO, 2016a). Class 4 is subjective ratings and uncalibrated devices, which the part excludes from network-level surveys (COTO, 2016a). Part E classifies texture profilers by mobility, pavement contact, principle of operation and wavelength range (section E.2.2, Table E.1) (COTO, 2016f). Part F groups deflection devices by the load they apply: static and slow-moving devices, vibratory deflectometers, FWDs and high-speed deflectometers (section F.2) (COTO, 2016g). Part G sorts pavement distress imaging systems into two classes (section G.2.6.2, Table G.4): Class 1 systems support detailed crack analysis, and Class 2 systems are essentially used for distress ratings (COTO, 2016h).

Only Parts C and G number their classes, and Part F's categories carry no accuracy ranking (COTO, 2016g). A class number is therefore ambiguous until the part letter is attached.

Why does TMH 13 Part B sit underneath the other parts?

Every reading from TMH 13 Parts C to G is useful only when it can be placed on the road, so Part B covers positioning for all of them. It describes GPS receivers and the inertial sensors and DMI that augment them, so that position is carried through where satellite reception fails (COTO, 2016c). The positioning-validation clauses of Parts C, D, E and F send the reader back to Part B, and Part E adds GPS checks of its own (COTO, 2016a) (COTO, 2016e) (COTO, 2016f) (COTO, 2016g). Part B also lists typical positioning faults, such as a wrong survey start or end, GPS jumps and spikes, and a wrong survey direction (COTO, 2016c).

Parts B to G then follow one layout: devices; calibration, validation and control testing; and operational and quality control procedures (COTO, 2016d). Calibration confirms single components such as a laser or a load cell. Validation confirms that equipment, operator and measurement protocol, working as one system on validation sections under normal survey conditions, give meaningful data; it checks accuracy (bias) and repeatability (scatter), which are different questions (COTO, 2016d) (COTO, 2016c). The insight on repeatability and uncertainty shows why one cannot stand in for the other.

How do the TMH 13 parts add up on one synthetic road?

Synthetic example. Every value is invented to show the counting, and none is a specification. Chainage is the distance along the road from its start. Road S7 is one lane from chainage 12.000 km to 18.000 km, so the surveyed length is 18.000 − 12.000 = 6.000 km, or 6,000 m. Suppose the contract asks for one combined record per 100 m, a deflection test point every 200 m and an image every 10 m.

Parts	Synthetic choice	Calculation	Result
C, D, E (texture)	One row per 100 m	6,000 ÷ 100	60 rows in one .cid file
F	Test point every 200 m, both ends included	6,000 ÷ 200 + 1	31 test points
G	Image every 10 m	6,000 ÷ 10	600 images

Check value: the .cid file should hold 60 rows, from 12.000–12.100 km to 17.900–18.000 km, with no gap or overlap. In TMH 18 (Draft Version 4), roughness, rutting and texture go into one .cid file only when all three were measured at the same time and place, because they share the road identifier, lane code, start km, end km and measurement date (COTO, 2014). A file of 59 rows, or rows that restart at 0.000 km, points first to the positioning faults Part B lists, not to the roughness device. TMH 22 Part D (sections D.4.3 and D.4.7) discusses reporting lengths (COTO, 2013), and the walkthrough on specifying a road condition survey covers how to choose one.

What evidence does each TMH 13 part leave behind?

What to keep is the set of records that lets a reviewer trace a number back to a device, a check and a place:

• Positioning: the operator-signed daily check list and the validation results for GPS, inertial sensors and the DMI (COTO, 2016c).
• Calibration and validation reports for the device used, naming the validation sections (COTO, 2016d).
• Control-test results, and a note of data re-measured after a failed test (COTO, 2016c).
• Data files with a definition sheet for every code, and a flag on files measured under unusual conditions (COTO, 2016e).
• Deflection records: test-point location, pavement and air temperature, applied load and the deflection at each sensor (COTO, 2016g).
• Images: a unique image identifier with its location, and the validation record for the imaging system (COTO, 2016h).

The walkthrough on checking a roughness survey on a validation section shows one of these checks in practice, and the insight on IRI interpretation in South Africa covers what an IRI value tells an owner.

What does TMH 13 not decide?

TMH 13 does not fix the specification. Part A states that the guidelines do not serve as a complete specification, so the contract sets intervals, acceptance criteria and report formats, drawing on the validation requirements in Parts B to G (COTO, 2016d). Nor does it select a treatment. Its interpretation aids, such as the rut depth evaluation criteria (Table A.3) and the deflection bowl categories (Table A.7), stay in TMH 13; this guide reprints no roughness range, rut criterion or deflection category (COTO, 2016d). Part A recommends bowl parameters for relative benchmarking, after Horak (2008) (Horak, 2008), which the reference page on FWD deflection bowls summarises.

TMH 13 also does not tie a device class to a road class. Part C pairs device types with survey frequency and data use (Table C.3) (COTO, 2016a), whereas TMH 22 Part D, section D.4.3, ties roughness device classes to road classes (COTO, 2013). And it does not replace TMH 9 (Committee Draft Final, May 2016), the manual for visual assessment of road pavements (COTO, 2016b). Part G points to TMH 9 and TMH 22 for classification, nomenclature and methods whatever technology records the road (COTO, 2016h). Part A's document-version clause says a committee draft has no legal standing, so cite the edition and let the contract name the one that applies (COTO, 2016d).

What are the common misreadings of TMH 13?

• Part F is Surface Deflection. The cover says so; the file name and Part A's list in section A.1.3 say only "Deflection" (COTO, 2016g) (COTO, 2016d).
• The data-format manual is TMH 18. TMH 13 Parts B (B.4.2), D (D.4.2) and G (G.3.1) and TMH 22 Part D point to "TMH 20" for data formats. TMH 22's reference list (section A.2) names it "Standard for Road Network Data", in an entry separate from TMH 18; that title is the running head of TMH 18 (Draft Version 4), and TMH 13 Part C (C.5.3) names TMH 18 (COTO, 2016c) (COTO, 2016e) (COTO, 2016h) (COTO, 2013) (COTO, 2014) (COTO, 2016a).
• Deflection units differ between documents. TMH 18 (Draft Version 4 and Committee Draft 5.0) labels its deflection fields nanometres, whereas TMH 22 (D.4.5) asks for micrometres, so state the unit on the definition sheet that travels with the file (COTO, 2014) (COTO, 2016i) (COTO, 2013).

Frequently asked

What does TMH 13 cover?

TMH 13 (also written TMH13), Automated Road Condition Assessments, is a South African road manual in the Technical Methods for Highways (TMH) series compiled under COTO, the Committee of Transport Officials. It has seven parts: concepts and planning, positioning, roughness, rutting, skid resistance and texture, surface deflection, and imaging. The Committee Draft Final of May 2016 describes how to plan, run and control each measurement.

Which part of TMH 13 covers FWD deflection?

TMH 13 Part F, Surface Deflection, covers deflectometers, including the falling weight deflectometer (FWD), the FWD calibration protocols and the strength parameters derived from the deflection bowl. The Part F file name says only Deflection, but the cover title is Surface Deflection, so cite it as TMH 13 Part F, Committee Draft Final, May 2016.

Is TMH 13 the same as TMH 9 or TMH 11?

No, TMH 13 is a different manual. TMH 9 is the manual for visual assessment of road pavements by people. TMH 11 sets out standard survey methods for land surveying (Version 3.0, April 2017). TMH 13 covers measurement with vehicle-mounted instruments, from traffic-speed profilers to the falling weight deflectometer (FWD). TMH means Technical Methods for Highways, so several manuals share the prefix, and the number and part letter identify the one meant.

Which TMH 13 parts define device classes?

In TMH 13, Part C defines four roughness measurement classes, Part E classifies texture profilers, Part F groups deflection devices by the load they apply, and Part G defines two classes of pavement distress imaging system. Parts B and D define no device classes. Because Class 1 in Part C is not Class 1 in Part G, quote a class number together with its part letter.

Does TMH 13 approve a device or a contractor?

No, TMH 13 approves neither device nor contractor. It describes calibration, validation and control testing, and Part A says the guidelines do not serve as a complete specification. The road authority writes the acceptance criteria into the contract and checks the validation evidence against them. TMH 13 is a committee draft with no legal standing, and RoadSense does not issue approvals for any device, survey or file.

Where do TMH 13 results go next?

TMH 13 results move into road asset management under TMH 22 Part D, which lists the measurements a road authority collects, and into the TMH 18 exchange formats. In TMH 18 Draft Version 4, roughness, rutting and texture share one Combined Instrument Data (.cid) file and deflection bowls use a .fwd file. Name the TMH 18 version whenever a file is described.

Where this connects

The next manual is TMH 22 Part D, which lists the surveillance measurements a road authority collects and sends the reader to TMH 13 for how each is planned, executed and controlled (COTO, 2013). After that comes TMH 18, which lists the file formats for submitting results; name its version, Draft Version 4 or Committee Draft 5.0, whenever a file is described (COTO, 2014) (COTO, 2016i).

References

1. COTO (2016a). TMH13: Automated Road Condition Assessments. Part C: Roughness. Committee Draft Final, May 2016. Original source.Sections C.2–C.5; Table C.5 is for calibration-section selection
2. COTO (2016c). TMH13: Automated Road Condition Assessments. Part B: Positioning. Committee Draft Final, May 2016. Original source.Positioning and distance measurement guidance
3. COTO (2016b). TMH9: Manual for Visual Assessment of Road Pavements. Part A: General. Committee Draft Final, May 2016. Original source.Section A.2: degree and extent
4. Horak (2008). Benchmarking the structural condition of flexible pavements with deflection bowl parameters. Journal of the South African Institution of Civil Engineering, 50(2), pp. 2–9. Original source.Relative structural benchmarking with deflection bowls
5. COTO (2016d). TMH 13: Automated Road Condition Assessments. Part A: General. Committee Draft Final, May 2016. Original source.Sections, tables and clauses are cited inline in each guide
6. COTO (2016e). TMH 13: Automated Road Condition Assessments. Part D: Rutting. Committee Draft Final, May 2016. Original source.Sections, tables and clauses are cited inline in each guide
7. COTO (2016f). TMH 13: Automated Road Condition Assessments. Part E: Skid Resistance and Texture. Committee Draft Final, May 2016. Original source.Sections, tables and clauses are cited inline in each guide
8. COTO (2016g). TMH 13: Automated Road Condition Assessments. Part F: Surface Deflection. Committee Draft Final, May 2016. Original source.Sections, tables and clauses are cited inline in each guide
9. COTO (2016h). TMH 13: Automated Road Condition Assessments. Part G: Imaging. Committee Draft Final, May 2016. Original source.Sections, tables and clauses are cited inline in each guide
10. COTO (2014). TMH 18: Road Asset Data Electronic Exchange Formats. Draft Version 4, October 2014. Original source.Sections, tables and clauses are cited inline in each guide
11. COTO (2016i). TMH 18: Road Asset Data Electronic Exchange Formats. Committee Draft 5.0, February 2016. Original source.Sections, tables and clauses are cited inline in each guide
12. COTO (2013). Draft TMH 22: Road Asset Management Manual. Draft, March 2013. Original source.Sections, tables and clauses are cited inline in each guide

Use the manual edition and project requirements that apply to your work. Worked examples use synthetic values and are not site-specific design advice.