Speed on German Highways in Heavy Rain

Highway traffic safety is adversely affected by precipitation, especially in areas with insufficient water drainage. The hydroplaning risk is mainly influenced by the thickness of the water film. An equally important parameter for the hydroplaning incidence is the driven speed. Several previous investigations on highways showed that road users reduce their speed during heavy rain. However, up to now the results were rarely differentiated any further according to type of precipitation (spray, rain, ...) and/or intensity of precipitation (quotient of precipitation quantity and time). Hence the question must be asked, to what extent road users reduce their speed in dependency of precipitation intensity and whether this speed lies below the hydroplaning (aquaplaning) speed. The hydroplaning speed indicates when tires must be expected to lose traction and ride on a cushion of water on the carriageway. It is possible to determine hydroplaning (aquaplaning) speeds in dependence on various factors. Amongst other factors, the degree of impairment is depending on the water film thickness on the carriageway. For the determination of water film thicknesses on carriageways as well as aquaplaning (or hydroplaning) speeds the software PLANUS has been developed within a research project. Within this present investigation the speed choice of free-flowing passenger cars riding the left lane was analysed for different intensities of precipitation. In a next step this actually driven speeds on the German motorways were compared to aquaplaning speeds – the speed at which tires looses traction and ride on a cushion of water. The results showed for 3 of the 9 measuring points randomly selected that the actually driven speed exceeded the critical hydroplaning speed (up to 30 km/h) at which tires could start hydroplaning on the water film. Various accident investigations have shown that wet road surface conditions lead to a distinct increase in accident risk as compared to a dry carriageway. This is especially true for superelevation development sections (where the superelevation rate goes through zero). In order to reduce the increased accident risk in superelevation development sections in wet condition, design, infrastructure or traffic engineering measures are necessary. It must be the target to reduce the accident risks in sections with hydroplaning risk, by creating sufficient reserves between actual and hydroplaning speeds.

• Corporate Authors:

  Polytechnic University of Valencia

  Department of Transportation, Camino de Vera
  Valencia,   Spain  46022
• Authors:
  • Hartz, Birgit
• Conference:
  • 4th International Symposium on Highway Geometric Design
  • Location: Valencia , Spain
  • Date: 2010-6-2 to 2010-6-5
• Publication Date: 2010

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; References; Tables;
• Pagination: 13p
• Monograph Title: 4th International Symposium on Highway Geometric Design, June 2-5, 2010, Valencia, Spain

Subject/Index Terms

• TRT Terms: Highway design; Highway safety; Highway traffic; Hydroplaning; Rain; Traffic engineering; Traffic speed
• Uncontrolled Terms: Rainfall intensity
• Geographic Terms: Germany
• Subject Areas: Highways; Safety and Human Factors; I82: Accidents and Transport Infrastructure;

Filing Info

• Accession Number: 01338157
• Record Type: Publication
• Files: TRIS
• Created Date: Apr 28 2011 1:01PM