The objective of this research is to review and to provide a draft of the bases for assessing the road grip.
For the measuring systems skiddometer / SRM is to clarify whether a new evaluation framework is necessary and if a breakdown by different road types is appropriate. In addition, to examine the scope of this research whether possibly the currently valid guideline for assessing the grip should be adapted or whether different benchmarks would appear for different road types, depending on the measurement speed.
For the measuring system SCRIM a new evaluation background for the national roads is to create and for measuring speeds 60 km / h and 80km / h are to develop appropriate benchmarks.
For this research the following procedure is provided:
- Critical review of existing data bases
- If necessary, carry out additional measurements
- Creating frequency distributions for the measuring systems skiddometer / SRM and SCRIM entirety and depending on the road type (motorways, main roads in urban areas or long distance) and the measured speed
- Review of the former evaluation background based on the quantile
- Investigation of a possible link between the grip values and the linings for highways on the one hand and for main roads on the other hand
- Assessment of the frequency distributions and create a recommendation for the evaluation of road grip.
- Recommendations for adapting and supplementing standard SN 640 511b
Findings and conclusions of the project
It could be stated that the average distribution of the skid resistance values on Swiss roads has changed very little between 1984 and 2009. The portions of the skid resistance level, which range from sufficient to well evaluated, showed up very similar in 2009 when compared to 1984.
The situation with the bad to insufficient skid resistance levels got worse in 2009 when compared to 1984. This means that there are more insufficient skid resistances in the total quantity of the skid resistance values in 2009 than were present in 1984. These values are more unfavorable than the demanded approximate values for the minimum skid resistance. In addition it showed up that the portions of the low, and thus, bad skid resistance values in 2009 have their origin in the category of major roads, while these skid resistance ranges in the high capacity roads in 2009 are nearly identical to those of the total data from 1984.
In comparison to the total data from 1984 and also compared with the high capacity roads, the major roads in 2009 have larger portions of bad skid resistance values. This means also that the worst 5% of the skid resistance values of this road category lie more unfavorably today than in 1984. Today there exist on the average worse skid resistance conditions than in 1984 with more major roads, which must be rated as unfavorable development. Therefore considerations for the separate definition of approximate values of the minimum requirements of the skid resistance for major roads and high capacity roads are to be employed. It is to be examined whether the requirements for major roads would be intensified with the purpose to affect the skid resistance level which is decreasing on these roads since 1984 positively on a long-term basis. By a definition of higher skid resistance minimum requirements on major roads, the requirements to sight distances could possibly be reduced.
Although accidents on wet lanes cannot be attributed to the lack of lane skid resistance alone, it is nevertheless undisputed that bad grip tractions extend braking distances and are thus safety-relevant. In many countries the minimum standard requirements are alike or similar to the ones in Switzerland, they are however, as e.g. in France, not overall fixed but arranged according to road type and local situation. It is intended to treat the traffic dependent locally different situations fairly. The obtained findings show that there are differences in