Predicting Travel Time Reliability using Mobile Phone GPS Data Dawn Woodard Cornell University Probabilistic forecasts of travel times on a road network can be used for risk-averse routing, for reporting travel time reliability to a user, or as a component of fleet vehicle decision-support systems. Many of these uses (such as those for mapping services like Bing or Google Maps) require predictions for arbitrary routes in the road network, at arbitrary times; the highest-volume source of data for this purpose is GPS data from mobile phones. We introduce a method ("TRIP") to predict the probability distribution of travel time on an arbitrary route in a road network at an arbitrary time, using GPS data from mobile phones or other probe vehicles. TRIP gives informed predictions for parts of the road network with little data, captures weekly cycles in congestion levels, and is computationally efficient even for very large road networks and datasets. We apply TRIP to predict travel time on the road network of the Seattle metropolitan region, based on GPS data from Windows phones. TRIP provides improved interval predictions (forecast ranges for travel time) relative to Microsoft’s engine for travel time prediction as used in Bing Maps. It also provides deterministic predictions that are almost as accurate as those from Bing Maps, despite using fewer explanatory variables, and differing from the observed travel times by only 10:4% on average over 36,493 test trips. To our knowledge TRIP is the first method to provide accurate predictions of travel time reliability for complete, large-scale road networks.