Accidents reported on the main carriageway of the 22 and a half mile stretch of the M4 motorway between Chiswick and Maidenhead Thicket have been analysed for the period from its completion in March 1965 to the end of 1967. Particular attention has been paid to the location of accidents along the length, the state of the road surface and whether skidding was reported, the numbers and types of vehicles involved and the direction in which they were travelling, and whether tyre failure occurred. Over the period studied there was a large increase in the amount of traffic and the number of accidents reported annually. Between 1966 and 1967 the overall increase in accidents was 44 per cent; a total of 463 accidents was reported in 1967. The accident rate per million vehicle miles on the main part of the M4 was of the same order as on other motorways (ie about 0.6 to 0.9) but on the elevated section the rate was about four times as high (2.7 to 3.7). Further, the accident rate on the eastbound carriageway of the elevated section was more than double that on the westbound. The skidding rates (ie the percentages of accidents in which skidding was reported) averaged 36 per cent when the road was dry and 60 per cent when it was wet. The dry road rate was of the same order as the National average for motorways, but the wet rate was more then 40 per cent higher than the National average for motorways. The incidence of skidding varied along the length of the motorway: in the wet particularly high rates occurred on the 2-lane asphalt section (Slough East to Maidenhead Thicket) and on part of the 3-lane asphalt section. Measurements showed that the wet road skidding resistance was low on these sections. (Author/publisher)
Abstract