1. 1 Segment Level Analysis of Travel Time Reliability Meead Saberi K., 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

5. 5 Definitions of Reliability  The consistency or dependability in travel times from day to day (1)  The variability between the expected travel time and the actual travel time (2)  The variability and predictability of travel times (3)

6. 6 What is TT Reliability? Average Travel Time Departure time: 17:00

7. 7 Average Travel Time What is TT Reliability? Departure time: 17:00

8. 8 Average Travel Time What travelers remember... What is TT Reliability? Departure time: 17:00

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  Lognormal Distribution  On-Time Travel: Γ(1.1*Mean)  Misery Index: Γ- ¹ (%85 th )/Mean - 1 (1) (4) (5)

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 Congestion Frequency Time Sensitivity Analysis Congested speed threshold: 35 mph

16. 16 Congestion Frequency Time Sensitivity Analysis Congested speed threshold: 40 mph

17. 17 Congestion Frequency Time Sensitivity Analysis Congested speed threshold: 45 mph

18. 18 Lognormal Distribution Departure time: 5 pm Average TT = 4:05 min 90%th TT = 7:36 min Milepost 305.12

19. 19 Lognormal Distribution Departure time: 8 am Average TT = 1:08 min 90%th TT = 1:11 min Milepost 305.12

20. 20 Conclusions  Travel time reliability substantially varies across freeway segments.  Arbitrary thresholds affect the reliability estimates.  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).

21. 21 Next Steps  Studying the relationship between the freeway corridor reliability and the reliability of its segments (a probability-based approach).  Studying the relationship between travel time reliability and the variability of flow and speed  How does reliability vary across lanes?  Which reliability measure will actually help managing our freeways?  Developing a model to estimate more reliable travel times for a corridor based on the historical segment travel times, flow and speed variability in each segment.

22. 22 Acknowledgment  Prof. Robert L. Bertini  Priya Chavan  PORTAL

23. 23 Questions?Questions? Thanks

24. 24 References 1. FHWA. Travel Time Reliability: Making It There On Time, All the Time. 2.Lomax, T., S. Turner, M. Hallenbeck, C. Boon, R. Margiotta, and A. O’Brien. Traffic Congestion and Travel Reliability: How Bad Is the Situation and What Is Being Done About it? FHWA. 3.Tu, H., Ir. J. W. C., van Lint, H. J., van Zuylen. Travel Time Reliability Model on Freeways. 87 th annual meeting of the Transportation Research Board, Washington D.C., 2008. 4.Emam, E. B., H. Al-Deek. Using Real-Life Dual-Loop Detector Data to Develop New Methodology for Estimating Freeway Travel Time Reliability. Transportation Research Record, No. 1959, Washington D.C., 2006, pp. 140-150. 5.NCHRP. Cost-Effective Performance Measures for Travel Time Delay, Variation, and Reliability. Report No. 618.