Analyzing Travel Time Reliability: Data and Analysis Methods

Over the past decade, travel time reliability has emerged as a key concept for assessing and managing the performance of the transportation system. Simply put, travel time reliability describes how personal mobility changes from day-to-day for trips made at the same time. Savvy commuters understand that travel times for their work trips, which tend to occur at roughly the same time every weekday, can vary based on a variety of conditions they encounter. Figure 1 shows that the interaction of disruptive events\u2014traffic incidents, inclement weather, special events, and work zones\u2014with daily demand, physical capacity, and traffic controls lead to different travel time experiences on different days. Travel time reliability describes the nature of this variability in travel times in terms of the quality, consistency, predictability, timeliness, and dependability of traveler experiences on the transportation system