Freeway Travel-Time Information: Design and Real-Time Performance Using Spot-Speed Methods

This paper shows that the precision of a freeway travel-time information system, in a real-time context, is not related solely to the accuracy of the measurement. Immediacy in reporting the information and forecasting capabilities play a role. Therefore, focusing only on the accuracy of the travel-time measurement is a myopic approach, which can lead to counter-intuitive results. Specifically, it is claimed that, using travel times estimated with the traditional spot-speed midpoint algorithm, the performance of the real-time information system when evolving traffic conditions prevail is better than using much more accurate directly measured travel times (MTTs). Guidelines for an adequate configuration of the common parameters of the system are provided. In addition, real-time context enhancements for travel-time estimation methods based on punctual speed measurements are proposed. These are addressed by taking into account an easy and practical implementation. They have been proven to work well in an empirical application on a Spanish freeway.