It is widely accepted that poor skid resistance on road surfaces is related to an increased risk
of accidents, especially in wet conditions. If a more consistent approach to skid resistance
policies is to be encouraged across Europe, then greater consistency of measurement is also
needed, which might be achieved by harmonising the various techniques currently used in
different countries. Also, some form of harmonisation is needed to meet the requirements of
CEN for future work on test methods for assessing road surfacing materials.
There has been a considerable amount of research into the possibilities for harmonising skid
resistance measurements over the years and Task 2.1 of the TYROSAFE project has
included a review of the state of the art. The review has focussed on work relating to
measurements on roads but similar work for measuring friction characteristics on airfields
has been included so that any cross-over of ideas could be taken into account.
The review has noted that there are various ways of approaching the problem. The concept
of harmonisation has been described as "the definition of a common scale, against which
measurements from different sources or standards based on different measurement types
can be compared and understood" or "the adjustment of the outputs of different devices used
for the measurement of a specific phenomenon so that all devices report the same value(s)
(i.e. report in a common scale), except for some inaccuracy". However, it has also been
recognised that if the inaccuracy, or imprecision, of a harmonised scale is too great for
practical purposes (and what is acceptable may vary with different purposes), it may not be
possible to harmonise measurements. Ultimately, standardisation might prove to be a better
technical solution for a particular purpose. TYROSAFE aims at the definition of a "common
scale" for skid resistance measurements, either through harmonisation or standardisation.
The main purposes for harmonised skid resistance measurements envisaged in this review
have been either for acceptance of new road surfacings or for in-service network monitoring
and maintenance planning. While formal harmonisation may not be necessary for
measurements made for research, (including accident investigation), there is potential
relevance to these fields also, since it is likely that researchers or accident investigators
might wish to understand their data in the context of conditions on the wider road network.
This review has concentrated on the harmonisation of measurements made in wet
conditions: the frictional properties of roads affected by ice or snow or contaminants other
than water are outside its scope.
The review considered a range of experimental studies into the problem of harmonisation,
which has been addressed to various degrees for many years. The main effort over the last
fifteen years or so has included three major studies, leading to proposals for harmonised
indices: the PIARC International experiment which led to the IFI (International Friction Index);
the HERMES experiment which assessed the proposed EFI (European Friction Index) and a
study on airfields that led to the IRFI (International Runway Friction Index). There have also
been numerous smaller exercises which have considered alternative approaches or
attempted to test or validate these ideas in some specific situations.
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created: Marco Conter, 14.07.2010 15:03:22 last modified: Marco Conter, 14.07.2010 15:56:59
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