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Influence of Probe Vehicle Sample Size on Expressway Travel Speed Estimation

In this paper, both real-world and simulation data of urban expressway networks are used to evaluate estimation performance of probe only and detector only travel speed estimation. A sampling statistics analysis shows that the accuracy of probe only estimates depends on two parameters: probe sample size n and traffic density D of corresponding expressway sections. A new concept form for MAPE (Mean Absolute Percentage Error), MAPE (n, D) = a(D) + b/n is suggested, where a is a function of D and b a constant. Also, a study on detector only estimates shows that estimation MAPE is a function of D only. Based on the relative performance of probe and detector only travel speed estimates, a weighted average model is proposed to combine probe and detector only estimates. A case study shows the advantages of the proposed data fusion model and the future perspective of applying probe data in expressway travel speed estimation.