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ii Congestion has long been a concern to transportation operation and planning. Various methods and technologies have been developed and applied in detecting congestion. This study focuses on using bus as probes to indicate recurrent congestion on urban roadway networks. In this study, bus speeds are used to reflect indications of congestion. Bus speed data collected over “homogeneous days ” are pooled in order to find indications of recurrent congestion. Bus speeds collected during a time period at each location are compared to bus speeds collected during other time periods (or during the whole day) at the same location. For practical purposes, the entire bus route investigated for the purpose of method development, validation, and demonstration is discretized into 10 meter spatial sections, and time of day is discretized into 30 minute time intervals. Each 10 meter long spatial section and 30 minute duration time interval constitutes a space-time cell for which existence or absence of an indication of congestion is determined