1. 1 Segment Level Analysis of Travel Time Reliability Meead Saberi K., Robert L. Bertini Portland State University I-5 SB, San Diego, CA

2. 2 Objectives  How can we measure travel time reliability?  How does reliability vary across freeway segments?  Identifying the locations and times in which travel time reliability drops

3. 3 Study Area I-5 Northbound Portland, OR

4. 4 Methodology  Breaking the overall I-5 NB into shorter segments: 22 segments from milepost 286.1 to 307.9  5-minute aggregated travel times for February and March 2007 from PORTAL (only weekdays)

5. 5 Definitions of Reliability  The consistency or dependability in travel times from day to day  The variability between the expected travel time and the actual travel time  The variability and predictability of travel times

6. 6 What is TT Reliability? Average Travel Time Departure time: 17:00 0 2 4 6 8 10 12 2/1/20072/12/20072/23/20073/7/20073/18/20073/30/2007 Time (January and February 2007) Travel Time

7. 7 What is TT Reliability? Departure time: 17:00 0 2 4 6 8 10 12 2/1/20072/12/20072/23/20073/7/20073/18/20073/30/2007 Time (January and February 2007) Travel Time Average Travel Time

8. 8 What travelers remember... What is TT Reliability? Departure time: 17:00 0 2 4 6 8 10 12 2/1/20072/12/20072/23/20073/7/20073/18/20073/30/2007 Time (January and February 2007) Travel Time Average Travel Time

9. 9 Measures of Reliability  90 th or 95 th Percentile Travel Time  Coefficient of Variation: Std/Mean  Travel Time Index: Mean/FFTT  Buffer Index: (%95 th - Mean)/Mean  Planning Time Index: %95 th /FFTT  Congestion Frequency  Skew: (%95 th - %50 th )/(%50 th - %10 th )  Width: (%95th - %50th)/%50th

10. 10 Coefficient of Variation Time

11. 11 Travel Time Index Time

12. 12 Buffer Time Index Time

13. 13 Planning Time Index Time

14. 14 Congestion Frequency Time Congested speed threshold: 30 mph

15. 15 0 0.5 1 1.5 286.1286.3289.4289.6290.5292.2 293.2293.7295.2296.3296.6297.3299.7301.1302.5303.9304.4305.1306.5307.5307.9 Segment Buffer Index 0 1 2 3 4 5 6 Planning Time Index Buffer Index Planning Time Index 0 0.5 1 1.5 2 2.5 286.1286.3289.4289.6290.5292.2 293.2293.7295.2296.3296.6297.3299.7301.1302.5303.9304.4 305.1306.5 307.5307.9 Segment Buffer Index 0 2 4 6 8 10 12 Planning Time Index Buffer Index Planning Time Index Segment Ranking

16. 16 Segment Ranking 0 4 8 12 16 286.1286.3289.4289.6290.5 292.2 293.2293.7295.2296.3296.6297.3299.7301.1302.5303.9304.4305.1306.5307.5307.9 Segment Skew 0 0.5 1 1.5 2 2.5 3 Width Skew Width 0 20 40 60 80 100 286.1286.3289.4289.6290.5 292.2293.2293.7295.2296.3296.6297.3299.7301.1302.5303.9 304.4305.1 306.5 307.5307.9 Segment Skew 0 1 2 3 4 5 Width Skew Width

17. 17 Conclusions  Travel time reliability varies across freeway segments.  Travel time reliability measures are inconsistent.  Using the segment travel time reliability measures in regional transportation planning and operations is beneficial for evaluating and prioritizing roadway segments (corridor-level analysis is not sufficient).

18. 18 Acknowledgment  Prof. Robert L. Bertini  Priya Chavan  PORTAL team at Portland State University

19. 19 Questions?Questions? Thanks