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FACTORS CONTRIBUTING TO LOW FRICTION BETWEEN WHEELS AND ROAD SURFACE

The Swedish Road and Traffic Research Institute was commissioned by the Road Construction Office of the Swedish Road Administration to analyse the results of various friction measurements in order to try to identify factors which can cause low friction between tyre and road surface. Friction is dependent on the macro- and microtexture of the road surface. A rough, harsh pavement (surface with both macro- and micro-texture) has high and even friction. Newly laid surface dressing without excess binder is one example of such pavement. A rough yet glossy pavement (surface with macro- but without microtexture) usually has considerably lower friction. Such a surface can develop, for example, from the preceding type when the aggregate becomes polished or when the microtexture is covered in some way. A smooth but harsh pavement (surface without macro- but with microtexture) , e.g. sand asphalt, can have very good friction characteristics in dry or slightly humid conditions while heavy rain or local water layers may reduce the braking efficiency catastrophically. There is a great risk of aqua-planing on such a surface. A very smooth and glossy pavement (surface lacking both macro- and microtexture), e.g. a bleeding surface dressing has low friction under damp and wet conditions even at speeds below 50 km/h. As a rule friction is dependent on speed. The dependence is minimal on dry, clean pavements, but can be considerable on wet and/or dirty surfaces. Speed dependence on pavements with smooth texture is more pronounced than on pavements with rough texture. High and even friction must obviously be sought for. Needless to say, this requirement also implies that friction characteristics should not vary greatly with time. Such a change in friction can arise, for example, when binder is gradually pressed up to the surface or when the pavement surface is heavily rutted (risk of aqua-planning). Hazardous, sudden friction changes may arise under some meteorological conditions if extreme differences in heat capacity occur along the road. A typical situation of this kind exists when ice is formed on a bridge but not on connecting sections of the road. Loose sand on a hard, firm road surface leads to a considerable reduction of friction. This may be a question, for example, of residual sand left after sanding to conjunction with winter maintenance or laying of pavements.

Language

  • Swedish

Media Info

  • Features: Tables;
  • Pagination: 18 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00097428
  • Record Type: Publication
  • Report/Paper Numbers: No. 52
  • Files: TRIS
  • Created Date: Aug 13 1975 12:00AM