Origin-Destination-Based Travel Time Reliability

Travel time reliability (TTR) is an important performance indicator for transportation systems. TTR can be generally categorized as either segment based or origin-destination (O-D) based. A primary difference between the two TTR estimations is that route information is implied in segment-based TTR estimations. Segment-based TTR estimations have been widely studied in previous research; however, O-D-based TTR estimations are used infrequently. This paper provides detailed insight into O-D-based TTR estimations and raises three new issues: (a) How many routes do travelers usually take and what are the TTR values associated with these routes? (b) Do statistical differences exist between route-specific and non-route-specific (NRS) TTR values? (c) How can O-D-based TTR information be delivered? Two processes were proposed to address the issues. Three TTR measures-standard deviation, coefficient of variation, and buffer index-were calculated. The bootstrapping technique was used to measure the accuracy of the TTR measures. Approximate confidence intervals were used to investigate statistically the differences between route-specific and NRS TTR measures. A large quantity of taxicab GPS-based data provided data support for estimating O-D-based TTR measures. The results of O-Dbased TTR measures showed that no statistically significant differences existed between route-specific and NRS TTR measures for most of the time periods examined. Statistically significant differences could still be found in some time periods. Travelers may take advantage of these differences to choose a more reliable route. Access to both numeric TTR values and route preference, instead of just to TTR information on segments of interest, can be beneficial to travelers in planning an entire trip.