A System for Displaying Travel Times on Changeable Message Signs

We present a system that displays travel time predictions in real time on changeable message signs (CMS) in California. Using loop detector data, this system calculates predicted travel times on designated routes every five minutes. An automated process displays the current travel time predictions on the appropriate CMS’s. We demonstrate the benefits of real time travel time prediction. Historical analysis show that route decision based on CMS almost always identifies the quickest route when alternates are available. Regardless of whether alternate routes exist, prediction reduces travel time uncertainly which is quantified by buffer time. The buffer time is the total time one must budget to guarantee a certain probability of being on-time, such as 90%. We verify the accuracy of loop detector data-based travel time estimates by comparing with probe vehicle travel times. There is a close agreement between the two when the data quality is high, and large errors when quality is low. Therefore, data quality of CMS routes must be verified by probe vehicle tests before deployment.