1. 1 The Effects of Weather on Freeway Traffic Flow Meead Saberi K. Priya Chavan Robert L. Bertini Kristin Tufte Alex Bigazzi 2009 ITE Quad Conference, Vancouver, B.C.

2. 2 Objectives PrecipitationVisibilityWind SpeedSpeedFlow

3. 3 Study Area I-5 NB Freeway Portland, OR MP 302.5 MP 305.12 MP 307.9

4. 4 Traffic Data Data Source: Portland Oregon Regional Transportation Archive Listing (PORTAL) Data Characteristics: Weekdays 2005, 2006 and 2007 (14,965 hours) Hourly aggregated dual-loop detector data Incident free hours

5. 5 Weather Data Data Source: National Oceanic and Atmospheric Administration (NOAA) Weather Station: Portland International Airport (PDX) Hourly rainfall, visibility and wind speed

6. 6 Weather Categorization Rainfall Classification: 1) No rain 2) Very light rain (0-0.01 in/hr) 3) Light rain (0.02-0.04 in/hr) 4) Moderate rain (0.05-0.16 in/hr) 5) Heavy rain (>0.16 in/hr) Total N = 14,965 N(1) = 13,389 N(2) = 602 N(3) = 572 N(4) = 371 N(5) = 31 Note: ‘No rain’ data excluded from plot

7. 7 Weather Categorization Visibility Classification: 1) High visibility (>5 mi) 2) Low visibility (≤5 mi) Total N = 14,965 N(1) = 14,084 N(2) = 881 Note: measurement maximum of 10 mi (excluded from plot)

8. 8 Weather Categorization Wind Speed Classification: 1) High wind speed (>15 mph) 2) Low wind speed (≤15 mph) Total N = 14,965 N(1) = 531 N(2) = 14,434

9. 9 Effects of Rainfall on Speed

10. 10 Statistical Significance Non-Parametric Kruskal-Wallis Test

11. 11 Effects of Rainfall on Mean Speed 17:00 Probabilistic Approach

12. 12 Effects of Rainfall on Mean Flow

13. 13 Statistical Significance Non-Parametric Kruskal-Wallis Test

14. 14 Effects of Rainfall on Mean Flow 17:00 Probabilistic Approach

15. 15 Effects of Visibility on Speed

16. 16 Statistical Significance Non-Parametric Mann-Whitney Test

17. 17 Effects of Visibility on Mean Flow

18. 18 Statistical Significance Non-Parametric Mann-Whitney Test

19. 19 Effects of Wind Speed  Wind speed effects on speed and flow were similar to visibility effects  High winds corresponded with low visibility

20. 20 Conclusions  We observed traffic changes with rain at these locations; amount varied with intensity and hour of day Speeds up to 7 mph lower when raining Flows up to 230 vph lower when raining  Effects not always statistically significant – relationship with congestion is unclear  Unknown seasonal influences  Unknown sensitivity to weather categorization

21. 21 Conclusions  We observed traffic changes with visibility at these locations; amount varied with hour of day Speeds up to 5 mph lower with low visibility Flows up to 150 vph lower with low visibility  Effects not always statistically significant  Unknown categorization sensitivity  Unknown seasonal influences  Possible correlation with rainfall effects

22. 22 Conclusions  We observed traffic changes with wind speed at these locations; amount varied with intensity and hour of day Speeds up to 6 mph lower with high winds Flows up to 170 vph lower with high winds  Effects not always statistically significant  Unknown categorization sensitivity  Unknown seasonal influences  Possible correlation with rainfall effects

23. 23 Next Steps  Work with higher resolution weather and traffic data (5-min aggregated weather data are also available)  Look at more sites  Sensitivity analysis of weather classification

24. 24 Questions?Questions? Thank you!