Runway surface thresholds and the documents that set them: ICAO, FAA, EASA and the test standards

Runway surface limits are set by different documents for different quantities. Evenness and texture appear in aerodrome design specifications, roughness in a United States Federal Aviation Administration (FAA) advisory circular, friction in maintenance guidance, and the test methods that define each measurement in ASTM and ISO standards. The International Civil Aviation Organization (ICAO) supplies the frame in Annex 14 Volume I, and national documents turn it into worked practice (ICAO, 2022a) (FAA, 2009) (EASA, 2025). This guide is engineering background, not operational guidance. It shows which document states which limit, in whose units and status, and where no limit exists.

Key facts

• ICAO Annex 14 Volume I supplies the frame for runway surface requirements, and national documents such as FAA advisory circulars, EASA CS-ADR-DSN and UK CAP 168 set out the worked practice.
• EASA CS-ADR-DSN Issue 7, GM1 ADR-DSN.B.090(a), gives no deviation greater than 3 mm under a 3 m straight-edge for a new runway surface.
• FAA AC 150/5380-9 (2009) places a Boeing Bump Index below 1.0 in the acceptable zone and above 1.0 in the excessive or unacceptable zone (paragraphs 2.4a and 2.5a).
• EASA CS ADR-DSN.B.090 specifies an average texture depth of not less than 1.0 mm for a new surface, and mean texture depth and mean profile depth are different quantities.
• The ICAO runway condition code is assigned from the runway condition assessment matrix (RCAM) in Doc 9981 Part II Chapter 2, not taken from a friction-device reading.
• No document cited in this guide sets a limit for a runway profile power spectral density class, dynamic wheel load or excitation frequency.

The concept map

The connections in text

1. Aerodrome design and operations (ICAO Annex 14) → Runway condition report (GRF) (ICAO Doc 9981): condition reporting
2. Aerodrome design and operations (ICAO Annex 14) → Friction and texture guidance (ICAO Doc 9137 Pt II): friction and texture guidance
3. Aerodrome design and operations (ICAO Annex 14) → Evenness and texture specification (EASA CS-ADR-DSN): EU transposition
4. Aerodrome design and operations (ICAO Annex 14) → UK licensing standards (UK CAP 168): UK transposition
5. Aerodrome design and operations (ICAO Annex 14) → Australian runway surface (CASA Part 139 MOS): Australian transposition
6. Aerodrome design and operations (ICAO Annex 14) → Canadian roughness guidance (TC AC 302-023): evenness figure adapted
7. Roughness and Boeing Bump Index (FAA AC 150/5380-9) → BBI computed in ProFAA (ProFAA): BBI computed
8. Roughness and Boeing Bump Index (FAA AC 150/5380-9) → Longitudinal profile (ASTM E950): profile input
9. Construction smoothness (FAA AC 150/5370-10H) → BBI computed in ProFAA (ProFAA): 12 ft straight-edge simulation
10. Friction and CFME (FAA AC 150/5320-12C) → Continuous friction (ASTM E2340): CFME family
11. Friction and texture guidance (ICAO Doc 9137 Pt II) → Continuous friction (ASTM E2340): CFME family (no citation)
12. Evenness and texture specification (EASA CS-ADR-DSN) → Mean profile depth (ISO 13473-1 / ASTM E1845): MPD via ISO 13473-1

Which documents set runway surface limits, and how do they connect?

Three tiers of document are involved. ICAO sets the frame: Annex 14 Volume I (Aerodrome Design and Operations, 9th edition, July 2022), Airport Services Manual Part II (Doc 9137, Pavement Surface Conditions, 4th edition, 2002) and PANS-Aerodromes (Doc 9981, 3rd edition, 2020) (ICAO, 2022a) (ICAO, 2002) (ICAO, 2020). States and regions write practice, and ASTM and ISO standards define how each quantity is measured.

Tier	Documents (edition)	What they set out
Frame	ICAO Annex 14 Vol I (9th ed., 2022); Doc 9137 Part II (4th ed., 2002); Doc 9981 (3rd ed., 2020)	Evenness, texture and friction guidance; the runway condition report
Practice	FAA AC 150/5380-9 (2009), AC 150/5370-10H (2018), AC 150/5320-12C (1997); European Union Aviation Safety Agency (EASA) CS-ADR-DSN Issue 7 (2025); UK CAP 168 (13th ed., 2025); CASA Part 139 MOS 2019 (Compilation No. 7, 2026); Transport Canada AC 302-023 (2016)	Roughness, smoothness, friction, evenness and texture in each State's wording (FAA, 2018) (FAA, 1997) (UK CAA, 2025a) (CASA, 2026) (Transport Canada, 2016)
Measurement	ASTM E950, E965, E1845, E2340; ISO 13473-1	Longitudinal profile, volumetric texture, mean profile depth, continuous friction (ASTM, 2022) (ASTM, 2024a) (ASTM, 2023a) (ISO, 2019) (ASTM, 2021b)

The map draws the same links, and each step has its own guide: surveying roughness on the centreline and wheel paths, the Boeing Bump Index against IRI and the straight-edge, macrotexture, friction and speed and the power spectral density of a runway profile. The rehabilitation step is the journey from runway survey to rehabilitation decision.

What does each document say about surface evenness and smoothness?

EASA's guidance material GM1 ADR-DSN.B.090(a) in CS-ADR-DSN Issue 7 gives no deviation greater than 3 mm under a 3 m straight-edge for a new surface, and UK CAP 168 (13th edition) paragraph 3.216 sets out a 3 m straight-edge test (EASA, 2025) (UK CAA, 2025a). In the 6th edition (2013), Annex 14 Volume I carried this guidance in Attachment A, section 5, "Runway surface evenness"; this guide prints no paragraph number for the current edition (ICAO, 2022a).

Construction smoothness is a different test with a different base. FAA AC 150/5370-10H (21 Dec 2018), paragraph 401-5.3g, lists contractor quality-control smoothness variances of less than 1/4 in in 12 ft, which is 6.35 mm in 3.66 m; it is a quality-control check, not an acceptance test (FAA, 2018). AC 150/5380-9 (2009), at 2.3b(1), cites the then-current 1/4 in in 16 ft (6.35 mm in 4.88 m); the current construction circular uses 1/4 in in 12 ft as a contractor QC check (FAA, 2009). Quote the edition with the number.

Narrated film · 2:32

Which document sets the limit

A map of ICAO, FAA, EASA and the test standards, then a units axis that sets each quoted limit in its own unit beside the SI value.

Read the film transcript

Who decides how smooth a runway has to be, and in which units? This guide maps which document sets which limit, and where none exists. The International Civil Aviation Organization, ICAO, sets the frame in Annex Fourteen Volume One, and two companion manuals. States then write practice: the American FAA, the European EASA, and the British CAP one six eight. ASTM and ISO standards define how each quantity is measured. For evenness, EASA guidance gives no deviation greater than three millimetres under a three metre straight-edge on a new surface. Construction smoothness differs: the FAA lists variances under a quarter of an inch in twelve feet, six point three five millimetres in three point six six metres. That is a quality-control check, not an acceptance test. Roughness is judged by its effect on the aircraft, using jet transports near rotation speed. The Boeing Bump Index is the largest ratio of measured bump height to acceptable height at that bump length. Deciding to operate, restrict or close a runway belongs to the aerodrome operator. EASA specifies an average texture depth of not less than one millimetre for a new surface. Mean texture depth and mean profile depth are different quantities, so a specification must say which it means. Friction is measured with continuous friction equipment, run at forty and sixty miles per hour over one millimetre of water. Friction levels belong to the device, not to the runway condition code. Some quantities have no threshold in any of these documents. Power spectral density class, dynamic wheel load, a runway roughness index limit and hydroplaning speed are all unset. Where no limit exists, a report says so rather than borrowing one. Aviation documents mix inches, feet, knots and g, so one relation does every conversion. Equation one: x sub S I equals x sub source times c. First, x sub S I, the value in S I units. Then x sub source, the value as printed in the document. Last, c, the exact conversion factor. A quarter of an inch times twenty-five point four millimetres per inch is six point three five millimetres. One hundred and thirty knots times zero point five one four four four four metres per second per knot is sixty-six point nine metres per second. The rotation-speed band runs from sixty-six point nine to one hundred and two point nine metres per second. Never convert inside a quoted threshold: quote it in the source unit, then give the conversion. Read each limit with its document, edition and locator, and the next guides apply them to the survey.

How does the FAA judge roughness, and what status does that carry?

FAA AC 150/5380-9 (Guidelines and Procedures for Measuring Airfield Pavement Roughness, 30 Sep 2009) defines airfield roughness by its effects on the aircraft: fatigue and wear, cockpit vibration, excessive vertical acceleration and reduced braking, not passenger ride (paragraphs 1.2b to 1.2e). Texture is not roughness (1.2g) (FAA, 2009). Its guidance rests on jet transports near rotation speed, 130 to 200 kt (66.9 to 102.9 m/s, paragraph 2.1).

The Boeing Bump Index (BBI) at a point is the largest ratio, over all straight-edge lengths, of the measured bump height to the acceptable limit at that bump length. A BBI below 1.0 lies in the acceptable zone; above 1.0 lies in the excessive or the unacceptable zone (paragraphs 2.4a and 2.5a, Figure 2-4). The circular describes the excessive zone as needing immediate repair but not closure, and the unacceptable zone as warranting immediate closure of the affected pavement (paragraphs 2.3b(2) and 2.3b(3)). These are the circular's definitions. Any decision to operate, restrict or close a runway belongs to the aerodrome operator under its State's rules. The circular is mandatory only for projects funded through the airport improvement and passenger facility charge programmes (Foreword and paragraph 2), and it addresses single events, not cyclic or harmonic ones.

Research statements stay labelled as research. An FAA-sponsored report (Gerardi and Gerardi, DOT/FAA/TC-23/09, January 2023) does not constitute FAA policy. It applies Boeing g criteria in which a peak vertical acceleration at the centre of gravity over 0.80 g (7.85 m/s²) is unacceptable (Table 1, p. 7) (FAA, 2023). A Dutch review calls a peak vertical acceleration at the landing gear below 0.35 to 0.40 g (3.43 to 3.92 m/s²) an achievable and acceptable objective, and adds that standard criteria are not yet available (NLR-TP-2009-190, pp. 9 to 10) (NLR, 2009). Transport Canada AC 302-023 paragraph 6.1(4) names four regions, while the original Boeing criterion has three zones, so name the source whenever zones are counted (Transport Canada, 2016).

What does the texture specification say, and how is texture measured?

EASA CS ADR-DSN.B.090 (Issue 7) specifies an average texture depth for a new surface of not less than 1.0 mm (0.039 in) (EASA, 2025). Annex 14 recommends a minimum texture depth for new surfaces, a Recommendation rather than a Standard; see the current edition for the paragraph and value (ICAO, 2022a).

Two measurements are easy to confuse. ASTM E965-15(2024) measures macrotexture depth by a volumetric technique, giving a mean texture depth (MTD) (ASTM, 2024a). ASTM E1845-23 and ISO 13473-1:2019 calculate a mean profile depth (MPD) from a measured surface profile (ASTM, 2023a) (ISO, 2019). MTD and MPD are different quantities, and moving between them needs a transformation whose coefficients this guide does not print. A specification should say which one its number means.

Where does friction sit, and how does it differ from the runway condition code?

Maintenance friction is measured with continuous friction measuring equipment (CFME); Doc 9137 Part II paragraph 3.2.5 gives a self-wetting water depth of at least 1 mm (ICAO, 2002). FAA AC 150/5320-12C, paragraphs 3-16 and 3-17, has approved CFME run at 40 mph (65 km/h) and 60 mph (95 km/h) with a uniform 1 mm (0.04 in, as the circular prints it) water depth, and a complete survey uses both speeds (FAA, 1997). The pair is nominal: the circular's 40 mph is 64.4 km/h and 60 mph is 96.6 km/h, so 65 and 95 km/h are rounded equivalents. ASTM E2340 is a continuous-friction test method (ASTM, 2021b).

Friction levels are device-specific. Doc 9137 Table 3-1 and AC 150/5320-12C Table 3-2 hold them; a value from either must name the device, tyre, pressure, speed and water depth, so no row is reprinted. The runway condition code in the Global Reporting Format (GRF) is a different thing: it is assigned from the runway condition assessment matrix (RCAM) in PANS-Aerodromes Part II Chapter 2, applicable from 4 November 2021, not taken from a friction-device reading (ICAO, 2020).

Which runway quantities have no threshold in any of these documents?

A report should say where no limit exists rather than borrow one.

• Power spectral density (PSD) class. ISO 8608:2016 reports road-profile data and covers roads, streets, highways and off-road terrain; runways are neither covered nor excluded, and this guide gives no class boundaries (ISO, 2016).
• Dynamic wheel load and excitation frequency. No cited document sets a limit. A 1959 NASA memorandum found gear loads greatest at impressed frequencies of 1.5 to 2 cycles per second; that is a finding from its own tests, not a limit (NASA, 1959).
• International Roughness Index (IRI) on a runway. ASTM E1926 is a road index (ASTM, 2021a). AC 150/5380-9 defines roughness by aircraft effects, and Transport Canada AC 302-023 paragraph 6.2 lists IRI as a complement to the bump method. That IRI alone does not describe aircraft response is this guide's own inference, and no runway IRI limit is quoted.
• Hydroplaning speed. The spin-down relation in NASA TN D-2056 (1963) is a fitted research relation, not a limit (NASA, 1963).

The power spectral density guide and the bump guide explain why these quantities describe a profile without ruling on it.

How do the units line up across these documents?

Aviation documents mix inches, feet, knots, miles per hour and g with SI. One relation does every conversion in this guide.

The formula, term by term: unit conversion to SI

Equation 1: x_SI = x_source × c, and in reverse x_source = x_SI ÷ c

symbol	what it is in words	unit	where its value comes from	typical range
x_source	the value as printed in the document	in, ft, kt, mph or g	the document locator in the text	lengths 0.25 in to 16 ft; speeds 40 mph to 200 kt; accelerations 0.35 to 0.80 g
c	exact conversion factor from the definition of the unit	mm/in, m/ft, (m/s)/kt, (m/s)/mph, (m/s²)/g	25.4, 0.3048, 0.514444, 0.44704, 9.80665	fixed by definition
x_SI	the same quantity in SI	mm, m, m/s, m/s²	product of the two	lengths 6.35 mm to 4.88 m; speeds 17.9 to 102.9 m/s; accelerations 3.43 to 7.85 m/s²

Where it comes from: the factors are definitions, not measurements, so Equation 1 is exact. The international inch is defined as 25.4 mm; a foot is 12 in, so 0.3048 m. A knot is one nautical mile (1852 m) per hour, so 1852 m / 3600 s = 0.514444 m/s. A mile per hour is 1609.344 m / 3600 s = 0.44704 m/s. Standard gravity is 9.80665 m/s².

Worked numbers (every input is printed in a cited document; none is synthetic): 0.25 in × 25.4 mm/in = 6.35 mm. 12 ft × 0.3048 m/ft = 3.66 m, and 16 ft = 4.88 m. 130 kt × 0.514444 (m/s)/kt = 66.9 m/s, and 200 kt = 102.9 m/s. In reverse, dividing by c: 1.0 mm ÷ 25.4 mm/in = 0.039 in (0.04 in at the circular's rounding). 0.35 g × 9.80665 m/s² = 3.43 m/s², 0.40 g = 3.92 m/s² and 0.80 g = 7.85 m/s². Converted to km/h, 40 mph = 64.4 km/h and 60 mph = 96.6 km/h, against the nominal 65 and 95 km/h. The script calc/units_axis.py prints each value.

What it means and where it stops: the conversion lets a reader set an inch-and-foot tolerance beside a metre-and-millimetre one, which informs how a scope or report quotes a limit. It does not make two numbers comparable. The 6.35 mm in 3.66 m smoothness check and the 3 mm under 3 m evenness test have different bases and purposes, and the circular's 40 and 60 mph pair is not the converted 65 and 95 km/h pair. Never convert inside a quoted threshold: quote it in the source unit, then give the conversion. The clauses that use these quantities are AC 150/5370-10H 401-5.3g, AC 150/5320-12C paragraphs 3-16 and 3-17, and AC 150/5380-9 paragraph 2.1.

Frequently asked

Which document sets the runway evenness requirement?

EASA's guidance material GM1 ADR-DSN.B.090(a) in CS-ADR-DSN Issue 7 gives no deviation greater than 3 mm under a 3 m straight-edge for a new surface, and UK CAP 168 (13th edition) paragraph 3.216 sets out a 3 m straight-edge test. In the 6th edition (2013), Annex 14 Volume I carried this guidance in Attachment A, section 5, "Runway surface evenness"; this guide prints no paragraph number for the current edition.

What does a Boeing Bump Index above 1.0 mean?

In FAA AC 150/5380-9 (30 September 2009), a Boeing Bump Index (BBI) below 1.0 is in the acceptable zone, and a BBI above 1.0 is in the excessive or the unacceptable zone, so a value above 1.0 is not automatically unacceptable. The circular defines the zones; decisions on operating a runway belong to the aerodrome operator under its State's rules.

What texture depth is specified for a new runway surface?

EASA CS ADR-DSN.B.090 (Issue 7) specifies an average texture depth of not less than 1.0 mm for a new surface. ICAO Annex 14 recommends a minimum for new surfaces. Mean texture depth from the ASTM E965 volumetric method and mean profile depth from ASTM E1845 or ISO 13473-1 are different quantities, so a specification should state which one it uses.

Is the runway condition code the same as a friction value?

No. The runway condition code in the ICAO Global Reporting Format is assigned from the runway condition assessment matrix in PANS-Aerodromes (Doc 9981) Part II Chapter 2, applicable from 4 November 2021. Maintenance friction is measured with continuous friction measuring equipment under ICAO Doc 9137 Part II and FAA AC 150/5320-12C, and its levels are device-specific.

Is there an IRI limit for runways?

None is quoted in the documents cited here. The International Roughness Index in ASTM E1926 is a road index. FAA AC 150/5380-9 defines airfield roughness by its effects on the aircraft, and Transport Canada AC 302-023 paragraph 6.2 lists IRI as a complement to the bump method, not as a limit.

Where this connects

The next guides apply these limits: surveying roughness on the centreline and wheel paths and AC 150/5380-9 explained. The physics of profile, wavelength and texture is shared with road practice; see IRI against rut depth and texture depth, lane and wheelpath conventions across manuals and checking a roughness survey on a validation section. For the road contrast see the TMH 13 IRI page and the SAPEM texture and skid page.

References

1. ICAO (2022a). Annex 14 to the Convention on International Civil Aviation, Aerodromes, Volume I, Aerodrome Design and Operations. 9th edition, July 2022, incl. Amendment 18 (adopted 4 Aug 2025, applicable 27 Nov 2025; some provisions later). Original source.Attachment A, 'Runway surface evenness' (no paragraph numbers: 9th-ed. numbering unverified)
2. FAA (2009). AC 150/5380-9, Guidelines and Procedures for Measuring Airfield Pavement Roughness. 30 Sep 2009, no revision letter, Active. Original source.Foreword; para 1.2b-g; para 2; 2.1; 2.2a-g; 2.3a-b; 2.4a-d; 2.5a-b; Fig 2-3; Fig 2-4; Ch 3 (3.1, 3.2)
3. EASA (2025). Certification Specifications and Guidance Material for Aerodrome Design (CS-ADR-DSN). Issue 7, 16 May 2025 (ED Decision 2025/004/R; applicable 24 May 2025; PDF corrected 16 Jun 2025). Original source.CS ADR-DSN.B.090 (a)-(d); GM1 ADR-DSN.B.090(a); GM1 ADR-DSN.B.191 (m)-(p)
4. ICAO (2002). Airport Services Manual, Part II, Pavement Surface Conditions (Doc 9137). 4th edition, 2002. Original source.Sections 1.5.10, 1.5.15-1.5.16, 2.3.1, 3.2.5, 3.2.9 and Table 3-1
5. ICAO (2020). Procedures for Air Navigation Services, Aerodromes (PANS-Aerodromes, Doc 9981). 3rd edition, 2020 (consolidates Amendment 3, applicable 5 Nov 2020); Amendment 5 applicable 27 Nov 2025 (OLS provisions 21 Nov 2030). Original source.Part II Chapter 2 (runway condition report, applicable 4 Nov 2021); table numbers unverified against the amended text
6. FAA (2018). AC 150/5370-10H, Standard Specifications for Construction of Airports. 21 Dec 2018, Active; errata 19 Aug 2020 (draft 10J not final). Original source.401-5.3g (p. 280); 401-6.2d; 401-6.2e; 401-8.1d; 501-4.12; 501-5.3g; 501-6.6b(4)
7. FAA (1997). AC 150/5320-12C, Measurement, Construction, and Maintenance of Skid Resistant Airport Pavement Surfaces. Base 18 Mar 1997; Change 9 dated 29 May 2025 (replaces App 4); Active. Original source.2-2; 2-15 to 2-22; 3-3 and Table 3-1; 3-16; 3-17; 3-19 and Table 3-2; App 4 (cite from 150-5320-12c-chg9.pdf)
8. UK CAA (2025a). CAP 168, Licensing of Aerodromes. 13th edition, July 2025, incorporating Amendment 15 (page version 13, re-issued 2 Dec 2025). Original source.3.210-3.217 (3.216 3 m straight edge); 3.214-3.215; 3.232-3.254
9. CASA (2026). Part 139 (Aerodromes) Manual of Standards 2019. Compilation No. 7, 12 May 2026 (F2026C00403). Original source.s 6.09 'Runway surface' (table numbers unverified in C07)
10. Transport Canada (2016). AC 302-023, Measurement and Evaluation of Runway Roughness. Issue 02, effective 16 Dec 2016 (current per TC page, checked 3 Nov 2026). Original source.4.3(3); 5.1-5.3; 6.1 with Fig 1 and Table 1; 6.2 (IRI, RMSVA, RCI)
11. ASTM (2022). Standard Test Method for Measuring the Longitudinal Profile of Traveled Surfaces (ASTM E950/E950M). E950/E950M-22. Original source.Scope 1.1
12. ASTM (2024a). Standard Test Method for Measuring Pavement Macrotexture Depth Using a Volumetric Technique (ASTM E965). E965-15(2024). Original source.Scope 1.1
13. ASTM (2023a). Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth (ASTM E1845). E1845-23. Original source.Scope 1.1-1.3, Note 1
14. ISO (2019). ISO 13473-1:2019, Characterization of pavement texture by use of surface profiles, Part 1: Determination of mean profile depth. 2019 (Ed. 2), confirmed 2024. Original source.Cited by EASA GM1 ADR-DSN.B.191(o)
15. ASTM (2021b). Standard Test Method for Measuring the Skid Resistance of Pavements and Other Trafficked Surfaces Using a Continuous Reading, Fixed-Slip Technique (ASTM E2340/E2340M). E2340/E2340M-11(2021). Original source.Scope 1.1-1.3, 1.6-1.8
16. FAA (2023). Method to Identify and Quantify Multiple-Event Roughness, DOT/FAA/TC-23/09 (T. Gerardi, M. Gerardi, APR Consultants). Final Report, January 2023 (does not constitute FAA policy). Original source.Exec summary pp. ix-x; Sec 2 p. 2; Sec 2.1-2.3 pp. 2-3; Sec 3 p. 4; Sec 3.1 p. 9; Table 1 p. 7; App E pp. E-3/E-4, E-8/E-9
17. NLR (2009). Evaluation Methods for longitudinal evenness of runway pavements: An overview of recent Dutch experiences, NLR-TP-2009-190 (P.A. van Gelder, M.J.A. Stet). June 2009. Original source.Sec 1 pp. 5-6; Sec 2.1 p. 7 and Table 1; 2.2; Elaborate Survey pp. 9-10; 3.1 p. 11; 3.3 p. 13; 3.5 p. 16; 4 p. 18
18. ISO (2016). ISO 8608:2016, Mechanical vibration, Road surface profiles, Reporting of measured data. 2016 (Ed. 2), confirmed 2021; systematic review may be in progress. Original source.Scope (roads, streets, highways, off-road; excludes rail; runways not mentioned)
19. NASA (1959). Study of Taxiing Problems Associated with Runway Roughness, NASA Memo 2-21-59L (B. Milwitzky). March 1959. Original source.PDF p. 3 (summary), p. 6
20. ASTM (2021a). Standard Practice for Computing International Roughness Index of Roads from Longitudinal Profile Measurements (ASTM E1926). E1926-08(2021). Original source.Scope 1.1-1.3
21. NASA (1963). Phenomena of Pneumatic Tire Hydroplaning, NASA TN D-2056 (W.B. Horne, R.C. Dreher). November 1963. Original source.Equations (3)-(5) and the assumptions under equation (5); Fig. 4; Hysteresis paragraph, p. 12

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