This report addresses the question "when did the failures of motorway earthworks found during the motorway slope condition survey (Perry,1989) occur?" The method adopted was to search historical aerial survey photographs for evidence of the failures. Its success depended upon finding suitable photographs of areas of interest - defined to be areas where significant large numbers of slips had occurred. Although not all areas of interest were studied, because insufficient suitable photographs were available, the method was established to be workable. The results indicate a wide variation in behaviour. The failure rates of cuttings show an (often sudden) increase. Embankments exhibit a variety of behaviours, but periods of low activity seem to be a real feature. Tables are given for various slope materials of average failure rates of cuttings and embankments over intervals of 5 years, which may have an application in the planning and financing of motorway maintenance.

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