Standards reference

SAPEM Surface Texture (MPD/ETD) and Skid Resistance (SFC)

Under SAPEM, macrotexture is measured as MPD and converted to estimated texture depth by ETD = 0.8 × MPD + 0.2 (mm), while skid resistance uses SFC lower limits by road feature from 0.35 (dual carriageway) to 0.55 (signalised approach) (SANRAL, 2014).

Last reviewed: July 2026 · Verified against SAPEM texture and friction guidance
ETD = 0.8 · MPD + 0.2  (mm)
where MPD = mean profile depth from a laser profilometer (ISO 13473-1 method); ETD approximates the volumetric sand-patch texture depth.
Table 1. SAPEM macrotexture classification
BandInterpretation
Very PoorInsufficient drainage texture
PoorMarginal texture depth
AdequateTarget texture condition
RoughNoise/ride trade-off — check surfacing

Interactive figure: drag Mean Profile Depth to watch Estimated Texture Depth track the fixed SAPEM relation ETD = 0.8 × MPD + 0.2 (mm), then test a measured Sideways Force Coefficient against the skid-resistance limit for the selected road feature — 0.35 for a dual carriageway/freeway, 0.45 for a general road, 0.55 for a signalised approach/junction — where compliance is simply SFC ≥ limit.

Figure 1. The SAPEM texture and skid-resistance judgement: Estimated Texture Depth as a deterministic linear transform of Mean Profile Depth (ETD = 0.8 · MPD + 0.2), and Sideways Force Coefficient compliance evaluated relative to the road feature. Drag the controls to explore. The texture ribbon marks the documented South African minimum acceptable macrotexture (ETD ≈ 0.9 mm, i.e. MPD ≈ 0.875 mm), below which wet friction falls sharply with speed (SANRAL / TRH 3).

Worked example — one section, two verdicts

  1. Laser survey gives MPD = 0.9 mm → ETD = 0.8 × 0.9 + 0.2 = 0.92 mm.
  2. The same section's measured SFC = 0.48.
  3. If the section is a signalised approach, limit = 0.55 → 0.48 < 0.55 → non-compliant, flag for surface treatment.
  4. If it is open dual carriageway, limit = 0.35 → 0.48 ≥ 0.35 → compliant.
Identical measurements, different verdicts — SAPEM skid compliance is a function of road feature risk, not a single universal number.

How RoadSense computes texture and skid compliance

RoadSense derives MPD directly from laser profilometer data captured per survey segment, applies the SAPEM ETD conversion automatically, and compares any available SFC measurement against the feature-specific lower limit for that section. Results are banded on the georeferenced project map and included in TMH 18 exports alongside IRI, rutting, and other condition indicators.

How is ETD calculated from MPD?

ETD is calculated from MPD using the SAPEM conversion formula ETD = 0.8 × MPD + 0.2, where both values are expressed in millimetres, allowing laser-measured macrotexture to be related to the Estimated Texture Depth scale historically produced by the sand-patch test.

What is the minimum skid resistance for a road?

There is no single minimum: SAPEM sets SFC lower limits that scale with road feature and braking demand, ranging from 0.35 on a dual carriageway up to 0.55 at a signalised approach, reflecting the higher friction needed where vehicles brake, turn, or stop.

What does MPD measure?

MPD, Mean Profile Depth, measures road surface macrotexture — the average depth of the peaks and valleys in the pavement surface profile as captured by a laser profiler — and is the primary input SAPEM uses to assess whether a surface has adequate texture to support wet-weather skid resistance.

References

  • South African National Roads Agency (SANRAL) (2014) South African Pavement Engineering Manual. 2nd edn. Pretoria: SANRAL.
  • International Organization for Standardization (2019) ISO 13473-1: Characterization of pavement texture by use of surface profiles — Part 1: Determination of mean profile depth. Geneva: ISO.
  • Committee of Transport Officials (COTO) (2016) TMH 9: Manual for Visual Assessment of Road Pavements. Pretoria: Department of Transport.

For the full set of survey standards RoadSense reports against, see the standards library, or contact RoadSense to discuss a texture or skid resistance assessment for your network.