Conclusions

An examination of SCANNER data collected on the Scottish Trunk Road network was carried out to consider the implications of transitioning from SMTD to MPD. Based on various analyses, the following conclusions can be drawn:

• A general linear relationship exists between SMTD and MPD for all the material types, particularly in the SMTD texture range of 0 to 1.5mm.
• The relationship is dependent on surface type.
• A single relationship, weighted to the proportion of each surface type present, could be used to move to the use of MPD.
• An exercise to assess the impact of moving from SMTD to MPD as a measure of texture indicates that the transition could be relatively smooth.
• The study suggests that the adoption of MPD may be more conservative in categorising texture for maintenance intervention compared to SMTD.
• A comparison with similar data collected by NH showed that the relationship between SMTD and MPD was similar but that the ratio or slope of the line was found to be greater in the NH study.
• As the relationship is seen to be dependent on surface type, the most plausible explanation is that Scottish materials produce different surface characteristics. Higher trafficking levels experienced in England could also be a contributing factor.
• It is recommended that prior to adopting MPD, its use should be assessed within current skid policy. Initial indications suggest that the use on MPD may result in a more conservative approach to assessing the risk of skidding accidents.