Predictions of Freeway Traffic Speeds and Volumes Using Vector Autoregressive Models

Short-term traffic prediction on freeways is one of the critical components of advanced traveler information systems. The traditional methods of prediction have used univariate Auto-Regressive Integrated Moving Average (ARIMA) time series models, based on the autocorrelation function of the time series of traffic variable at a location; however, the effect of upstream and downstream location information has been largely neglected or underutilized in the case of freeway traffic prediction. It is the purpose of this article to demonstrate the effect of upstream as well as downstream locations on the traffic at a specific location. To achieve this, a section of five stations extending over 2.5 miles on I-4 in the downtown region of Orlando, Florida is selected. The speeds from a station at the center of this location are then checked for crosscorrelations with stations upstream and downstream. Cross correlation function is analogous to autocorrelation function extended to two variables. It indicates whether the past values of an input series influence the future values of a response series. It was found that the past values of upstream as well as downstream stations influence the future values at a station and, therefore, can be used for prediction. A vector auto regressive model was found appropriate and better than the traditional ARIMA model for prediction at these stations.