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 Universitymeead@pdx.eduhttp://web.cecs.pdx.edu/~meead/