Considerable errors exist in speed data that is obtained from various detectors, and its accuracy directly affects the results of various traffic analysis models. This research implemented 12 groups of field experiments on roads of different classes by using a test vehicle with GPS modules. It attempts to verify the accuracy discrepancy of travel speed data collected by a floating car system, microwave detectors, and loop detectors. Analysis shows that the average travel speed errors of floating cars on road sections of urban expressways and arteries are 13.6% and 27.8%, respectively, and the collected data and the actual speed have the same distribution. Compared with actual speed, the errors of the microwave detector on expressways and loop detectors on arteries are 30% and 56%, respectively. Although there exists a certain degree of error, basically, it can characterize the traffic conditions on the road section when the road section speed of the microwave detector is used to denote the travel speed. Study results provide suitable data sources for different traffic models that have different accuracy requirements. Besides, it provides a theoretical basis for improving data accuracy and completeness by using the redundant information of multi-source data. As the traffic congestion becoming increasingly serious, accurate and timely releasing of traffic information as well as reasonable traffic forecasts and guidance have gotten more and more attention. As one kind of the most important data of the Intelligent Transportation System, the accuracy of road section speed directly impacts the ITS application effect. Many kinds of detectors have been used for collecting road section speed, and the three most common are the floating car system, loop detectors, and microwave detectors. The floating car system can provide road section speed, but its accuracy has not been systematically validated. Currently, the literature (Jiang, Chang, Zhang 2009) just validated the accuracy of a single test vehicle by using different time intervals and upload times, but it wasn't for the whole system. Literature (Hu and Wen 2008) compared taxi speed and the travel speed of traffic flow by using the vehicle license plate method that theoretically obtained the precision of the floating car collection method, but it didn't involve the actual accuracy validation of the floating car collection system. Making the Beijing floating car collection system as the research object, by using a test vehicle, this research verified the accuracy of the system and analyzed the error distribution as well as the reasons affecting the data accuracy.
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