measurements of sideway-force coefficient carried out during 1967 and 1968 showed that the skidding resistance of the elevated section of the m4 motorway had fallen to a relatively low level. analysis of accident records also showed a high proportion of "skidding" accidents when the road was wet. the road was surface dressed during the summer of 1969 using aggregates that were expected to give a sustained high resitance to skidding. before treatment the sfc ranged between 0.35 and 0.45 at 50 km/h. in the three years following treatment the range lay between 0.50 and 0.60. during the two years following treatment there has been a reduction of 45 per cent in the total number of accidents with an even greater reduction in the number of accidents in which skidding was reported to have occurred. the accident record of this road before and after surface dressing emphasises the close relation between resistance to skidding and accidents on busy roads, and the beneficial effect of remedial treatment with aggregate of high resistance to polishing in such situations.(a).

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