Limit skid resistance values

In order to assure road safety, countries have implemented intervention or threshold skid resistance limit values (levels) that, when reached, would require immediate action for surface skid resistance restoration. 

Certain countries have also implemented investigatory or warning limit values. When the skid resistance reaches the assigned level, the pavement segment is systematically monitored, so that the restoration of its skid resistance is programmed in a timely manner. 

The intervention or investigatory levels depend on the road site category and its geometry and differ from country to country, even if skid resistance is monitored with the same device. Indicative limit values used in some countries are given in Table 16.7. 

In the United Kingdom, skid resistance monitoring is treated with greater rigor than some other countries. UK standards (Highways Agency 2004) use only investigatory levels in 

Country Instruments Warning value (investigatory level) Threshold value (immediate action limit) 

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The measurements taken by each device are not completely comparable. For this reason, the limiting values of skid resistance values set by national specifications should be differentiated for every device recommended to be used. This problem can be resolved by expressing the skid resistance value obtained with respect to the Skid Resistance Index (SRI) (see Section 16.3.6). 

The investigatory limit values of the characteristic SCRIM coefficient (CSC) at 50 km/h per site category are given in Table 16.8. The CSC is an estimate of the underlying skid resistance once the effect of seasonal variation has been taken into account (Highways Agency 2004). 

Finally, when PTVs are used to justify skid resistance safety limits, the values given in Table 16.9 may be used. 

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