WATER ON THE ROAD
WATER OP DE WEG
Over the years the Netherlands State Road Laboratory has always made efforts to collect and utilize information on the factors affecting the longitudinal and shear forces that can be transmitted between a road surface and the tyres of vehicles travelling on it. Water as a factor in this problem received attention in 1975 and 1976. This attention was prompted mainly by the unfavourable effect that the presence of water on road surfaces has upon the safety of motorized road users. From accident statistics in the Netherlands it emerges that in recent years nearly three times as many fatal road accidents occurred, per million vehicle-kilometres travelled, on wet road surfaces as on dry ones. Besides results of measurements carried out by the State Road Laboratory, this report also contains information derived from the Dutch and foreign technical literature. It is shown that the thickness of the film of water on the highway pavement is a good indicator of the degree to which the road user experiences the presence of water on the road as objectionable. The objectionable character may be due to reduction of the available longitudinal and shear forces developed between tyre and road surface, so that the risk of skidding is increased, and may also be due to visual impairment of the information that the motorist seeks to obtain, and needs, in properly performing his task as a driver. Considerable attention has been devoted to the thickness of the water film and to the factors that affect treatments, and the use of porous asphalt. Besides the formula found in the literature is to be preferred for calculating the thicknesses of water films and explains why. The use of the preferred formula is illustrated with the aid of a few examples. The State Road Laboratory performed measurements of longitudinal force coefficients on five highway pavement surfaces, the principal variables in these measurements being the water film thickness, the surface roguhness, and the speed of the vehicle. In addition to presenting and analysing the results of the measurements, the report also devotes somewhat more wide-ranging attention to the forces that occur at the contact area between tyre and road surface during braking and/or travelling along curves. From the results of the measures it appears, inter alia, that water films of even only a few millimetres thickness can cause very considerable reduction of the forces available at the contact area. Calculations show that such thicknesses regularly occur. The measures aimed at combating this water problem on roads, as described in the report, are therefore more particularly concerned with reducing the thickness of the film.
Study Centre for Road Construction, Netherlands14a Jansbuitensingel
- WELLEMAN, A G
- Publication Date: 1977-9
- Features: Figures; References; Tables;
- Pagination: 76 p.
- TRT Terms: Asphalt; Braking; Fatalities; Films (Coatings); Highway safety; Motor vehicles; Pavement grooving; Pavements; Rolling contact; Roughness; Shear stress; Skidding; Speed; Texture; Traffic speed; Water; Wet weather
- Uncontrolled Terms: Longitudinal; Shear forces; Wet pavements
- Old TRIS Terms: Grooves; Highway pavement; Water film
- Subject Areas: Highways; Pavements;
- Accession Number: 00173899
- Record Type: Publication
- Files: TRIS
- Created Date: May 31 1978 12:00AM