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DD CEN TS 15901 — Road and Airfield Surface Skid Resistance Standard Series
Road and Airfield Surface Characteristics — Part 6: Sideway Force Coefficient Method (SFCS): SCRIM® / Part 7: Longitudinal Fixed Slip Ratio Device (LFCG): GripTester® (CEN/TS Series)
🛣️ DD CEN/TS 15901 is a CEN Technical Specification issued by BSI in the Draft for Development (DD) series, specifying methods for measuring the skid resistance of road and airfield pavement surfaces. Skid resistance is directly related to driving safety: insufficient friction between tyres and a wet pavement significantly increases accident risk. Parts 6 and 7 of this series cover two main families of continuous friction-measuring devices — SCRIM® (sideway force coefficient method, SFCS) and GripTester® (longitudinal fixed slip ratio method, LFCG). UK participation was entrusted to Technical Committee B/510/5 (Surface characteristics), classified under ICS 93.080.20 (Road construction materials).
💡 The core challenge of skid-resistance measurement is to “reproducibly approach real tyre–pavement friction”: different devices (sideway/longitudinal force, slip ratio, test speed, water-film thickness) give different values, so the real work of the standard is to strictly prescribe equipment configuration, test speed, water volume, and data handling to make results comparable.
1. Series Overview and Application Context 📌
Pavement skid resistance changes with traffic polishing, material deterioration, and environmental conditions, and must be periodically measured to guide maintenance decisions. Continuous friction-measuring vehicles can collect data over long distances at normal traffic speeds, making them the main tool for network-level skid monitoring. The CEN/TS 15901 series defines unified “measurement procedures” for each device type; Parts 6 and 7 in this batch are the procedural documents for SCRIM and GripTester. The two families characterise skid level by the sideway force coefficient (SFCS) and the longitudinal force coefficient (LFCG) respectively.
2. Series Structure and Document List 📋
| Standard | Edition | Device / Method | Characteristic |
|---|---|---|---|
| DD CEN/TS 15901-6 | 2009 | SCRIM® (sideway force method) | Sideway force coefficient SFCS |
| DD CEN/TS 15901-7 | 2009 | GripTester® (longitudinal fixed slip ratio method) | Longitudinal force coefficient LFCG |
3. Part 6: SCRIM Sideway Force Coefficient Measurement 🔧
Part 6 specifies the SCRIM (Sideways-force Coefficient Routine Investigation Machine) method: a test wheel runs with a 20° yaw angle at a constant test speed while a watering system lays a prescribed water-film thickness ahead of the wheel; sensors continuously record the sideway force between tyre and pavement, converted to the sideway force coefficient (SFCS). The standard specifies in detail:
- Equipment calibration: periodic verification of sensors, water volume, and wheel load.
- Test speed and watering: run at the standard speed and maintain the water-film thickness.
- Data acquisition and averaging: sampling intervals, distance averaging, and result output.
- Quality assurance: reference sections and equipment self-check procedures.
⚠️ Water volume and vehicle speed are the two sensitive parameters for SCRIM results: insufficient water or abnormal speed shifts the water-film thickness from specification and distorts results. Periodically verify calibration per the standard and state test conditions in the report.
4. Part 7: GripTester Longitudinal Fixed Slip Ratio Measurement 🔍
Part 7 specifies the GripTester® (a longitudinal fixed slip ratio device) method: the test wheel spins longitudinally with a fixed slip ratio (about 15%) on a watered pavement surface, measuring longitudinal friction, converted to the longitudinal force coefficient (LFCG). GripTester is lighter than SCRIM and can be towed by a small vehicle, making it suitable for testing local sections, ramps, and lower-class roads. The standard likewise specifies calibration, watering system, speed control, data averaging, and result reporting, establishing a comparable basis with SCRIM-type devices.
💡 Results from different devices cannot be used interchangeably: in engineering, “equivalent conversion” or a common benchmark section is used to map LFCG/SFCS onto a unified skid indicator (e.g., the UK PSV/Mu framework) before comparing against thresholds.
5. Engineering Practice 🛠️
- 🔍 Network-level skid monitoring: routinely survey motorways and major roads to identify low-friction sections.
- 🔧 Maintenance decisions: compare SFCS/LFCG with maintenance thresholds to schedule resurfacing, milling, or anti-skid treatment.
- 📊 Airfield pavement assessment: runway friction testing and assessment (in line with international civil aviation requirements) for flight safety.
- 📋 Acceptance and tracking: acceptance testing of new/renewed pavements and long-term performance tracking.
6. Frequently Asked Questions ❓
❓ Q: Why are standards needed for multiple skid-measuring devices?
A: Different devices have different principles (sideway vs longitudinal force), speeds, and water-film conditions, each suited to different scenarios (network survey vs local inspection); prescribing procedures separately ensures each result is reliable.
A: Different devices have different principles (sideway vs longitudinal force), speeds, and water-film conditions, each suited to different scenarios (network survey vs local inspection); prescribing procedures separately ensures each result is reliable.
❓ Q: Can SFCS and LFCG be compared directly?
A: No. They are physically different and must be cross-referenced through a common benchmark and conversion relationships, using consistent reference worn/smooth sections for calibration.
A: No. They are physically different and must be cross-referenced through a common benchmark and conversion relationships, using consistent reference worn/smooth sections for calibration.
❓ Q: Does testing in rain matter?
A: The measurement aim is precisely to simulate wet conditions; the standard’s own watering system guarantees the water-film thickness, whereas natural rain gives uncontrolled films, so controlled conditions per the standard should be used.
A: The measurement aim is precisely to simulate wet conditions; the standard’s own watering system guarantees the water-film thickness, whereas natural rain gives uncontrolled films, so controlled conditions per the standard should be used.
🔍 Q: When do skid values abnormal drop?
A: Pavement polishing, bitumen bleeding, and surface contamination (oil/mud) all lower the friction coefficient; record surface condition before testing and rule out systematic error (calibration, water film, speed).
A: Pavement polishing, bitumen bleeding, and surface contamination (oil/mud) all lower the friction coefficient; record surface condition before testing and rule out systematic error (calibration, water film, speed).