Evaluation of the Accuracy of a Real-Time Travel Time Prediction System in a Freeway Construction Work Zone

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Abstract
The accuracy of the travel times displayed by the real-time Travel Time Prediction System (TIPS) in a construction work zone was investigated. The TIPS includes changeable message signs (CMSs) displaying the travel time and distance to the end of the work zone to motorists. The travel times displayed by the CMSs are computed by an intelligent traffic algorithm and travel time estimation model of the TIPS software, which takes input from strategically placed microwave radar sensors that detect the vehicle traffic on each lane of the freeway. Besides the CMSs and the radar sensors, the TIPS includes the computer and microcontroller computing the travel times, 220-MHz radios for transmitting data from the sensors to the computer and from the computer to the CMSs, and trailers with solar panels and batteries to power the radar sensors, CMSs, and radios. The evaluation included an accuracy analysis between the predicted and actual recorded travel times. Three crews driving independently of each other in the traffic stream recorded predicted and actual travel times at three CMSs to the end of the work zone for 12 h each day for three consecutive days, resulting in 119 trial runs. On the basis of the regression analysis of actual times versus predicted times, on the average the system does a reasonable job of predicting the travel times to the end of the work zone. About 88% of the actual times recorded for each sign, and for all the signs combined, were within a range of ±4 min of the predicted time. However, a few differences (actual versus predicted) as great as 18 min were observed. It is concluded that the realtime TIPS represents a definite improvement over any static non-realtime display system. It provides, in general and most of the time, useful and relatively accurate travel time predictions to the motoring public.

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