Real-time estimation of travel speed using urban traffic information system and filtering algorithm

Travel speed is an important parameter for measuring road traffic. urban traffic information system (UTIS) was developed as a mobile detector for measuring link travel speeds in South Korea. However, UTIS incur errors, such as those caused by irregular vehicle trajectories and communication delays. This study describes an algorithm developed for estimating reliable and accurate average roadway link travel speeds using UTIS data. The algorithm estimates link travel times using a robust data-filtering procedure to identify valid observations within a sampling interval using a varying data validity window. The size of the data validity window varies as a function of the standard deviation of observations in previous intervals. A field test showed that the variance of the percent errors of link travel times was reduced when measured using the new model. Therefore it can be concluded that the proposed model significantly improves travel speed measuring accuracy.