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The Effects of Weather on Freeway Traffic Flow

The Effects of Weather on Freeway Traffic Flow

Meead Saberi K.Priya Chavan

Robert L. BertiniKristin Tufte

Alex Bigazzi2009 ITE Quad Conference , Vancouver, B.C.

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ObjectivesObjectives

Precipitation

Visibility

Wind Speed

Speed

Flow

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Study AreaStudy Area

I-5 NB FreewayPortland, OR

MP 302.5MP 305.12MP 307.9

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Traffic DataTraffic 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 dataIncident free hours

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Weather DataWeather Data

Data Source:National Oceanic and Atmospheric Administration (NOAA)

Weather Station:Portland International Airport (PDX)Hourly rainfall, visibility and wind speed

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Weather CategorizationWeather Categorization

Rainfall Classification:1) No rain2) Very light rain (0-0.01 in/hr)3) Light rain (0.02-0.04 in/hr)4) Moderate rain (0.05-0.16 in/hr)5) Heavy rain (>0.16 in/hr)

Total N = 14,965N(1) = 13,389N(2) = 602N(3) = 572N(4) = 371N(5) = 31

Note: ‘No rain’ data excluded from plot

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Precipitation (0.01 inch/hour)

Freq

uenc

y (h

ours

)

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Weather CategorizationWeather Categorization

Visibility Classification:1) High visibility (>5 mi)

2) Low visibility (≤5 mi)

Total N = 14,965N(1) = 14,084N(2) = 881

Note: measurement maximum of 10 mi

(excluded from plot)

0

100

200

300

400

0 1 2 3 4 5 6 7 8 9

Visibility (mile)

Freq

uenc

y (h

ours

)

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Weather CategorizationWeather Categorization

Wind Speed Classification:1) High wind speed (>15 mph)

2) Low wind speed (≤15 mph)

Total N = 14,965N(1) = 531N(2) = 14,434

0

1000

2000

3000

4000

5000

6000

7000

0-5 5-10 10-15 15-20 20-25 25-30

Wind Speed (mph)

Freq

uenc

y (h

ours

)

9

25

35

45

55

65

0 1 2 3 4 5 6 7 8 9 10 11Time of Day

Med

ian

Spee

d (m

ph) No Rain Very Light Light Moderate

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35

45

55

65

0 1 2 3 4 5 6 7 8 9 10 11

Med

ian

Spee

d (m

ph)

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55

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0 1 2 3 4 5 6 7 8 9 10 11

Med

ian

Spee

d (m

ph)

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35

45

55

65

0 1 2 3 4 5 6 7 8 9 10 11

Med

ian

Spee

d (m

ph)

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12 13 14 15 16 17 18 19 20 21 22 23

Time of Day

Med

ian

Spee

d (m

ph)

25

35

45

55

65

12 13 14 15 17 18 19 20 21 22 23

Effects of Rainfall on SpeedEffects of Rainfall on Speed

25

35

45

55

65

12 13 14 15 17 18 19 20 21 22 2325

35

45

55

65

12 13 14 15 17 18 19 20 21 22 23

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Statistical SignificanceStatistical SignificanceNon-Parametric Kruskal-Wallis Test

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Time of Day

P-va

lue

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Effects of Rainfall on Mean SpeedEffects of Rainfall on Mean Speed

17:00

Probabilistic Approach

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25

50

75

100

10 20 30 40 50 60

Average Speed (mph)

1 - C

umul

ativ

e D

istr

ibut

ion

Func

tion

(%) No Rain

Rainy

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Effects of Rainfall on Mean FlowEffects of Rainfall on Mean Flow

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800

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2000

0 1 2 3 4 5 6 7 8 9 10 11

Time of Day

Med

ian

Flow

(vph

) No RainVery LightLightModerate

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Time of Day

Med

ian

Flow

(vph

)

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0

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Statistical SignificanceStatistical SignificanceNon-Parametric Kruskal-Wallis Test

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Time of Day

P-va

lue

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Effects of Rainfall on Mean FlowEffects of Rainfall on Mean Flow

17:00

Probabilistic Approach

0

25

50

75

100

800 1000 1200 1400 1600 1800

Average Flow (vph)

1 - C

umul

uativ

e D

istri

butio

n Fu

nctio

n (%

)No RainRainy

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Effects of Visibility on SpeedEffects of Visibility on Speed

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Time of Day

Ave

rage

Spe

ed (m

ph)

Low Visibility High Visibility

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Statistical SignificanceStatistical SignificanceNon-Parametric Mann-Whitney Test

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Time of Day

P-Va

lue

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Effects of Visibility on Mean FlowEffects of Visibility on Mean Flow

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200

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600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Time of Day

Ave

rage

Flo

w (v

eh/h

r)

Low VisibilityHigh Visibility

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400

600

800

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1200

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2000

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Statistical SignificanceStatistical SignificanceNon-Parametric Mann-Whitney Test

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Time of Day

P-Va

lue

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Effects of Wind SpeedEffects of Wind Speed

Wind speed effects on speed and flow were similar to visibility effects

High winds corresponded with low visibility

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200

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600

800

1000

1200

1400

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12 13 14 15 16 17 18 19 20 21 22 23Time of Day

Flow

(veh

/hr)

Low Wind Speed High Wind Speed

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ConclusionsConclusionsWe 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

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ConclusionsConclusionsWe 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

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ConclusionsConclusionsWe 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

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Next StepsNext 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

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Questions?Questions?Questions?

Thank you!