The Effects of Weather on Freeway Traffic Flow

Transcription

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

2 Objectives Precipitation Visibility Speed Flow Wind Speed 2

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

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 4

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

6 Weather Categorization 600 Total N = 14,965 Rainfall Classification: 1) No rain 2) Very light rain ( in/hr) 3) Light rain ( in/hr) 4) Moderate rain ( in/hr) Frequency (hours) N(1) = 13,389 N(2) = 602 N(3) = 572 N(4) = 371 N(5) = 31 5) Heavy rain (>0.16 in/hr) Note: No rain data excluded from plot Precipitation (0.01 inch/hour) 6

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

8 Weather Categorization 7000 Wind Speed Classification: 1) High wind speed (>15 mph) 2) Low wind speed ( 15 mph) Frequency (hours) Total N = 14,965 N(1) = 531 N(2) = 14, Wind Speed (mph) 8

9 Effects of Rainfall on Speed Median Speed (mph) No Rain Very Light Light Moderate 25 Median Speed (mph) Time of Day Time of Day 9

10 Statistical Significance Non-Parametric Kruskal-Wallis Test P-value Time of Day 10

11 Effects of Rainfall on Mean Speed 1 - Cumulative Distribution Function (%) Probabilistic Approach 100 No Rain Rainy Average Speed (mph) 17:00 11

12 Effects of Rainfall on Mean Flow Median Flow (vph) Median Flow (vph) No Rain Very Light Light Moderate Time of Day Time of Day 12

13 Statistical Significance Non-Parametric Kruskal-Wallis Test P-value Time of Day 13

14 Effects of Rainfall on Mean Flow Probabilistic Approach 1 - Cumuluative Distribution Function (%) 100 No Rain Rainy Average Flow (vph) 17:00 14

15 Effects of Visibility on Speed 70 Low Visibility High Visibility Average Speed (mph) Time of Day 15

16 Statistical Significance Non-Parametric Mann-Whitney Test P-Value Time of Day 16

17 Effects of Visibility on Mean Flow Low Visibility High Visibility Average Flow (veh/hr) Time of Day 17

18 Statistical Significance Non-Parametric Mann-Whitney Test P-Value Time of Day 18

19 Effects of Wind Speed Wind speed effects on speed and flow were similar to visibility effects High winds corresponded with low visibility Low Wind Speed High Wind Speed Flow (veh/hr) Time of Day 19

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 20

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 21

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 22

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 23

24 Questions? Thank you! 24