Different Impacts of Independent Recurrent and Non-Recurrent Congestions on Freeway Segments

This paper proposes a method that can be used to analyze the independent impacts of recurrent and non-recurrent congestion on freeway networks. The authors note that there have been few studies of these types of congestion, due both to the lack of traffic data collected during the episodes of congestion as well as the difficulty of using simulation tools effectively. The authors' proposed methodology is based on an elaborately calibrated simulation analysis, using the real traffic data obtained during the recurrent and non-recurrent congestion periods. The authors also summarize the evaluation results from the field tests of two intelligent transport system (ITS) technologies, which were developed to provide drivers with the real-time traffic information under the traffic congestion. The two technologies considered are TIPS (Traffic Information and Prediction System), a portable system enabling to estimate and display travel times to the motorists approaching a critical freeway segment (e.g., work-zone area); and ASIS (Advanced Speed Information System), which obtains speed data from downstream sensors, calculates travel speeds, and displays the speed and traffic information on an upstream portable changeable message sign (PCMS). They caution that the accuracy of these results may not be guaranteed during the transition periods such as the non-recurrent congestion. They present results of data from 2000 collected on highway segments in the state of Maryland (United States). The authors conclude that current ITS technologies still have significant problems in predicting and providing real-time traffic information, particularly under the fluctuating traffic conditions like during congestion periods.