Short period manual counts of less than twenty-four hours duration are commonly used to measure traffic flow at particular sites. In a previous report, SR 514, the accuracy of the estimates of total annual flow from a single short period count was examined. Recommendations were given for the most appropriate length and timing of these counts. In this report, the previous work has been extended to cover the estimation of flow for individual vehicle categories. In addition, the value of mounting two counts, one in August and one in a neutral month, has been investigated. Recommendations are given for the appropriate timing of counts and methods of estimation. (A)

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