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Due to the expansive use of GPS, GPS data can be used to provide valuable travel time and the travel speed data for the traffic information system. However, to access ID number for personal car would have problems with privacy. Thus, mean travel speed (MTS), which requires individual vehicle tracking, cannot be calculated directly. In this research, we try to estimate the MTS of the road by using GPS data without ID number. The estimation is done by considering the relationship between MTS and time mean speed (TMS), and experiment with relation between MTS and estimated space mean speed (eSMS). In addition, vehicle speed has high variance on inner city roads. Therefore, we proposed grouping method of spot speed data on the road segment, which is called segmentation, to reduce the traffic variance and analyze the collected data for MTS estimation. The results show the correlation between TMS and MTS is 0.94 and the relationship graphs between TMS and MTS have a linear trend line. Hence, TMS and MTS are very correlative. In summary, MTS estimation can be improved and developed into the model or equation if TMS is calculated under short segment (50 m), low traffic variance data, and under suitable time period (5 minutes).