1. Empirical Analysis of the Effects of Rain on Measured Freeway Traffic Parameters Meead Saberi K. and Robert L. Bertini Transportation Research Board Annual Meeting January 11, 2010

2. Background Clarus Initiative (2005): –U.S. Department of Transportation –FHWA Road Weather Management Program –National Oceanic and Atmospheric Administration (NOAA)

3. Objectives Quantify a measurable effect of weather conditions on traffic flow and speed Quantify possible effect of rainfall on incident occurrence

4. Study Area I-5 Northbound, Portland MP 302.5 (Broadway St.), MP 305.12 (Portland Blvd.), MP 307.9 (Jantzen Beach)

5. Data PORTAL

6. Weather Data Portland Oregon Regional Transportation Archive Listing (from NOAA) 17,301 hours on weekdays 2005-07 Hourly rainfall, wind speed, and visibility from PDX Airport

7. Traffic and Incident Data Portland Oregon Regional Transportation Archive Listing (from Oregon DOT) 26,000 hours on weekdays 2005-07 Hourly traffic volumes and speeds 2,700 reported incidents

8. Rain vs. No Rain No Rain = 15,402 hours Rain = 1,899 hours

9. Hourly Flow with and without Rain at MP 302.5

10. Hourly Speed with and without Rain at MP 302.5

11. Do incidents influence the results? Milepost 302.5

12. Do incidents influence the results? Milepost 302.5

13. Breaking the rainy condition into different rainfall categories Very Light = 692 hours Light =709 hours Moderate = 459

14. Effect on Incidents Occurrence From milepost 300 to 307.9

15. Examining Traffic Data in Different Rainfall Categories

17. Testing Differences Kruskal-Wallis Test Speeds Flows

18. Probabilistic Analysis MP 302.5

19. Probabilistic Analysis MP 302.5

20. Traffic and Weather Analysis in the Context of the Fundamental Diagram MP 302.5

21. Bivariate Analysis MP 302.5

22. Conclusions 1.Reported incident rates were higher for hours preceeded by 3 consecutive hours of rain than hours preceeded by no rain. 2.Higher reported incident rate was observed in moderate rain conditions. 3.The presence of incidents may slightly influence the analysis. 4.Differences of less than 10 mph in median traffic speeds and differences less than 190 vph in median flows were observed. 5.The probability of having higher speeds and flows in hours with rain was lower than during hours with no rain for congested time periods. 6.The 95% highest flow decreased by about 40–140 vph during hours with rainfall. 7.For slower speeds, a smaller difference between median flows in rainy and no rain conditions is observed than higher speeds.

23. Acknowledgements Prof. Robert Bertini Prof. Kristin Tufte Priya Chavan Rafael J. Fernández-Moctezuma Jerzy Wieczorek

24. Thank you! Meead Saberi K. Graduate Research Assistant ITS Lab, Portland State University meead@pdx.edu http://web.cecs.pdx.edu/~meead/