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Empirical Analysis of the Effects of Rain on Measured Freeway Traffic Parameters
Meead Saberi K. and Robert L. Bertini
Transportation Research Board Annual MeetingJanuary 11, 2010
Background• Clarus Initiative (2005):
– U.S. Department of Transportation– FHWA Road Weather Management
Program – National Oceanic and Atmospheric
Administration (NOAA)
Objectives• Quantify a measurable effect of weather
conditions on traffic flow and speed
• Quantify possible effect of rainfall on incident occurrence
Study AreaI-5 Northbound, Portland
MP 302.5 (Broadway St.), MP 305.12 (Portland Blvd.), MP 307.9 (Jantzen Beach)
Data
PORTAL
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
Traffic and Incident Data
Portland Oregon RegionalTransportation Archive Listing(from Oregon DOT)
• 26,000 hours on weekdays 2005-07• Hourly traffic volumes and speeds• 2,700 reported incidents
Rain vs. No Rain
No Rain = 15,402 hoursRain = 1,899 hours
Hourly Flow with and without Rain
at MP 302.5
Hourly Speed with and without Rain
at MP 302.5
Do incidents influence the results?
Milepost 302.5
Do incidents influence the results?
Milepost 302.5
Breaking the rainy condition into different rainfall categories
Very Light = 692 hoursLight =709 hoursModerate = 459
Effect on Incidents Occurrence
From milepost 300 to 307.9
Examining Traffic Data in Different Rainfall Categories
Examining Traffic Data in Different Rainfall Categories
Testing DifferencesKruskal-Wallis Test
Speeds Flows
Probabilistic AnalysisMP
302.5
Probabilistic AnalysisMP
302.5
Traffic and Weather Analysis in the Context of the Fundamental Diagram
MP 302.5
Bivariate Analysis MP 302.5
Conclusions1. 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.
Acknowledgements
Prof. Robert BertiniProf. Kristin TuftePriya ChavanRafael J. Fernández-MoctezumaJerzy Wieczorek
Thank you!
Meead Saberi K.Graduate Research AssistantITS Lab, Portland State [email protected]://web.cecs.pdx.edu/~meead/