At 11:39 14/11/2004, you wrote
Dear Friends,
Following the ongoing discussions on various forums on the web I would
like to share with you some information which I believe may substantiate
that dry spell may cause reduction in skid resistance and eventually may
lead to the "FIRST RAIN SKIDDING ACCIDENTS" phenomena. We have
been conducting many Pendulum tests on our highways during summer. In
many cases we encounter a gradual increase in the BPN values during the
testing process which is based on wetting-testing
cycles.
Sir,
Hope my reply is not to incoherent as it was written after 20 minutes of
power tool use (with a bad hangover)...
This was topic was also recently reported on in New Scientist late last
year or earlier this year, Californian researcher (or at least U.S.) I
understand
reported...........
The findings are along the lines of those reported on in 1929(?) by RRL (
nor TRL) in Research Report ONE :)
The polishing effect of an accumulation of fine debris on the road as a
mechanism for reducing skid resistance was studied and reported on in
1964(?) again by RRL ( I have a very brown faded paper
somewhere!)
it has been discussed on other lists too.....
http://lists.cc.utexas.edu:8000/guest/archives/SUPERPAVE/superpave.99c10/msg00001.html
< note one of the authors! you get around>
The cyclicity and variability
of network wide skid resistance week on week month on month year on year
will be written on for years to come
however the association you describe appears to have been reported on
independently by many........
plenty of reports on the cyclicity of skid resistance, the ones on the
development of SCRIM leading to the Northern Hemisphere May-September
testing season resulted form this study
However your findings may well be of value for the climatic regime of
Israel which may well be unique
Sadly the New Scientist Archives are for members only, i will search on
ZETOC tomorrow for this
http://zetoc.mimas.ac.uk/, today is a car restoration and pub day
:)
John
Typical values we measure
(during the testing) are:
30, 35, 42, 48, 50, 51, 51, 50…..
By the way, I think the ASTM E 303 recommends disregarding the
first measurement (I would appreciate explanation for this
guidance!) ,
Refer to road note 27 maybe, operation of the pendulum, again I might
have me a copy in the office, suggest swings 1 and 2 might align the
slider and/or remove any surface debris grit etc.... I assume the
readings are temperature corrected and the slider rubber is less than a
year old? <sorry>
but even if the first lowest
number is omitted there seems to be a gradual building-up of skid
resistance values process which is accompanied visually by cleaner
appearance during the recurrent wetting. Our assumption is that this
process may duplicate the actual phenomenon on the road even though I am
not sure which of the measured numbers represent correctly the pavement
surface condition (the ASTM standard , as I understand it, looks at
"stable values
I think the 1964(?) TRL report will be of great value in understanding
the mechanism, "they" collected detritus from the road surface
and generate the 2 gradings that are now used in the PSV test!!!! one
coarse (winter) one fine (summer), think it even looked at collisions
after a long dry spelll
Since (unless you talk to me about MY research) you will be told all
roads are at their worst in the wet with respect to skid resistance the
fact you make measures in dry spells using a wet test are of great value
and with the vehicles running on dry roads these low levels of wet
friction are "dormant" and not "exploited" and yes
you would have an increase in crashes in the middle of a long dry spell
on the one day it rained ;) (probably), can you go back and compare old
weather forecasts for the last 10 years with the rate of crashes say
within 3 miles of the raingauge? BUT only look at crashes where lack of
skid resistance rather than poor visibility was a contributory
factor....
zone"( in the above
example the 50-51 values) as the basis for decision on the
"correct" value. I would like to have comments how to treat
these values).
For those of you who are still doubtful about this issue, I would like
also to refer you to the following book:
CRONEY, D., and CRONEY, P., "THE DESIGN AND PERFORMANCE OF ROAD
PAVEMENTS", 2ND. ED,. 1991.,MCGRAW-HILL,
In this book, on page 529, in fig 27.8 present SFC values measured before
and at various times following the commencement of rain. The lowest
values are those measured as soon as the rain starts. It is interesting
note that these measurements were conducted in about 1936! An interesting
discussion on this issue is presented in this book on the following
page.
Road Note or Research Report 1 would be worth a look, I have a copy of
the microfiche somewhere, it was in 2 parts
Thanks for your
comments!
Mon plaisir!
Will post back tomorrow, [please contact me off list Shimon too]
