1. Temporal Aggregation Effects on ITS Data Freeway performance measures 1ITS Data Aggregation Effects – Alex Bigazzi Alex Bigazzi, Portland State University Helène Siri, ENTPE, France Dr. Robert Bertini, Portland State University

2. Objectives 2ITS Data Aggregation Effects – Alex Bigazzi Emissions, Fuel Consumption Speed Distribution Delay Travel Time Shockwaves, speed-flow diagrams Traffic States Effects of time-aggregating traffic data on common applications

3. Data Sources 3ITS Data Aggregation Effects – Alex Bigazzi ~2 miles of M4 in London Individual arrival times and speeds 24hr data over 5 weeks (1998) 500 meter spacing Loop Detectors 1,650ft of I-80 in CA 45min of data Each vehicle in all 6 lanes From NGSIM dataset Video- derived Trajectories

4. 4ITS Data Aggregation Effects – Alex Bigazzi

5. SPEED DISTRIBUTIONS 5ITS Data Aggregation Effects – Alex Bigazzi

6. Speed Consolidation 6ITS Data Aggregation Effects – Alex Bigazzi

7. 7 Speed Consolidation Emissions Fuel Consumption Safety

8. TRAVEL TIME 8ITS Data Aggregation Effects – Alex Bigazzi

9. 9 Endpoint method of travel time estimation

10. 10ITS Data Aggregation Effects – Alex Bigazzi x t Travel Sampling Error True Trajectory Speed-Estimated Trajectory Detector Sampling Error (I)

11. 11ITS Data Aggregation Effects – Alex Bigazzi x t Travel Grouped Speed Error Individual Speed Trajectories Average Speed Trajectory Detector Grouped Speed Error (II)

12. 12ITS Data Aggregation Effects – Alex Bigazzi 1 week of speeds Arithmetic Mean Speed (mph) Harmonic Mean Speed (mph) Arithmetic Mean Speed Error (III)

13. 13ITS Data Aggregation Effects – Alex Bigazzi

14. Estimate space mean speed from time mean speed Rearranging: 14ITS Data Aggregation Effects – Alex Bigazzi Ref: Lindveld and Thijs

15. 15ITS Data Aggregation Effects – Alex Bigazzi

16. DELAY Combined effects of speed distribution and travel time errors 16ITS Data Aggregation Effects – Alex Bigazzi

17. 17ITS Data Aggregation Effects – Alex Bigazzi 80 60 40 20 0 Speed 4:008:0012:00 16:00 20:00 FFS

18. One week of delay (loop data) 18ITS Data Aggregation Effects – Alex Bigazzi Disaggregate

19. 19ITS Data Aggregation Effects – Alex Bigazzi

20. TRAFFIC STATES AND SHOCKWAVES 20ITS Data Aggregation Effects – Alex Bigazzi

21. Identifying local max 21ITS Data Aggregation Errors – Alex Bigazzi Time (min)

22. 22ITS Data Aggregation Effects – Alex Bigazzi x t v min v max Travel x1 x2 Loop Data

23. Error in estimated shock speed

24. Speed-Flow Diagram

25. Conclusions 25ITS Data Aggregation Effects – Alex Bigazzi Masks more extreme speeds Underestimates emissions, fuel Small errors in delay Speed Distribution Helps est. from sampled speeds Harmonic mean crucial for delay Can est. from TMS and variance Travel Time Shockwave speed/TT error Fundamental diagrams – scale of interest Traffic States

26. ITS Data Considerations Weigh costs of aggregation vs. data mgmt.Future uses for data – can’t get it back!Missing or bad data Method of aggregation Record fidelity Other summary stats Variance Harmonic mean Median 26ITS Data Aggregation Effects – Alex Bigazzi

27. Thank you! 27ITS Data Aggregation Effects – Alex Bigazzi Acknowledgements Dr. Robert Bertini, Helene Siri, Stuart Beale, Tim Rees, and OTREC