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 Objectives PrecipitationVisibilityWind SpeedSpeedFlow

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

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

6 Weather Categorization Rainfall Classification: 1) No rain 2) Very light rain ( in/hr) 3) Light rain ( in/hr) 4) Moderate rain ( 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 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 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 Effects of Rainfall on Speed

10 Statistical Significance Non-Parametric Kruskal-Wallis Test

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

12 Effects of Rainfall on Mean Flow

13 Statistical Significance Non-Parametric Kruskal-Wallis Test

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

15 Effects of Visibility on Speed

16 Statistical Significance Non-Parametric Mann-Whitney Test

17 Effects of Visibility on Mean Flow

18 Statistical Significance Non-Parametric Mann-Whitney Test

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

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 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 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 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 Questions?Questions? Thank you!