A Framework for Defining and Estimating Travel Time Reliability

This paper provides an overview of the research conducted to-date to develop a framework for defining and estimating travel time reliability, for Florida’s Strategic Intermodal System (SIS). The objectives of this paper are a) to select an appropriate approach for measuring and reporting travel time reliability, and b) to develop a framework for estimating travel time reliability for freeway networks. This study investigated several potential definitions for travel time reliability. The definition recommended is as follows: “Travel time reliability is defined as the percent of trips that reach a destination over a designated facility within a given travel time (or equivalently, at a given travel speed or higher).” This definition allows for comparisons of travel time reliability over time, and across different facilities and different modes. The paper also presents a framework for obtaining travel time reliability with or with out travel time data. When travel time data are available, the travel time distribution can be directly constructed, and reliability as well as variability can be easily obtained. For cases when travel time data are not available, the paper presents preliminary models for estimating travel times and travel time reliability.