This study, based on an analysis of 6 months of records (amounting to 3945 records) held on the London Metropolitan Police congestion file, has examined the frequency and the importance of the different types of incident which have led to traffic congestion. The analysis has grouped the different types into three classes and identified that about up to 30% of incidents would allow some degree of pre-planning for minimising congestion. The study also includes an analysis of journey time records during a number of car journeys to work, some of which were affected by incidents. In terms of ranking the types of incidents which cause congestion, road traffic accidents (28.2%), roadworks (25.1%), and vehicle breakdowns (11%) are major causes of congestion. Although the study is based on traffic conditions in London it is thought that the findings will have application to urban areas generally.

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