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

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

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

4ITS Data Aggregation Effects – Alex Bigazzi

SPEED DISTRIBUTIONS 5ITS Data Aggregation Effects – Alex Bigazzi

Speed Consolidation 6ITS Data Aggregation Effects – Alex Bigazzi

7 Speed Consolidation Emissions Fuel Consumption Safety

TRAVEL TIME 8ITS Data Aggregation Effects – Alex Bigazzi

9 Endpoint method of travel time estimation

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

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

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

13ITS Data Aggregation Effects – Alex Bigazzi

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

15ITS Data Aggregation Effects – Alex Bigazzi

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

17ITS Data Aggregation Effects – Alex Bigazzi Speed 4:008:0012:00 16:00 20:00 FFS

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

19ITS Data Aggregation Effects – Alex Bigazzi

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

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

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

Error in estimated shock speed

Speed-Flow Diagram

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

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

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