As part of a programme of research at TRRL concerned with the investigation of accessibility techniques, an analysis has been carried out of the changes in accessibility which are likely to occur as a result of the construction of the M25 motorway. Four types of access (to jobs, retail jobs, employed residents and people) were studied, using travel times by car as a measure of travel difficulty. Similar patterns of accessibility and change in accessibility were found for all four types of access. The M25 was found to have little effect on levels of accessibility in London. Its effect was concentrated in a ring around London and centred on the M25; in this ring improvements were found in the accessibility indices used of between 20 and 50 per cent. The M25 was found to increase the number of jobs to which workers have access; however there was some evidence to suggest that there was also an increase in competition for jobs. The data sets used are typical of those collected for any travel demand model and the approach adopted here could be applied without difficulty to any area for which such a model has been set up. (A)

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