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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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Objectives

Precipitation

Visibility

Wind Speed

Speed

Flow

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Study Area

I-5 NB Freeway

Portland, ORMP 302.5MP 305.12MP 307.9

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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 dataIncident free hours

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Weather 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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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

)

Weather Categorization

Rainfall Classification: 1) No rain 2) 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

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0

100

200

300

400

0 1 2 3 4 5 6 7 8 9

Visibility (mile)

Freq

uenc

y (h

ours

)

Weather 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)

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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

)

Weather 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

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Effects of Rainfall on Speed

25

35

45

55

65

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

Time of Day

Med

ian

Spee

d (m

ph)

No Rain Very Light Light Moderate

25

35

45

55

65

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

Time of Day

Med

ian

Spee

d (m

ph) No Rain Very Light Light Moderate

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Statistical 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-v

alue

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Effects of Rainfall on Mean Speed

17:00

Probabilistic Approach

0

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 Flow

0

400

800

1200

1600

2000

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

Time of Day

Med

ian

Flow

(vph

)

No Rain Very Light Light Moderate

0

500

1000

1500

2000

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

Time of Day

Med

ian

Flow

(vph

)

No Rain Very Light Light Moderate

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Statistical 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-v

alue

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Effects 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 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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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 23

Time of Day

P-Va

lue

Statistical SignificanceNon-Parametric Mann-

Whitney Test

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Effects of Visibility on Mean Flow

0

200

400

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 Visibility High Visibility

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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 23

Time of Day

P-Va

lue

Statistical SignificanceNon-Parametric Mann-

Whitney Test

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Effects of Wind Speed

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

High winds corresponded with low visibility

0

200

400

600

800

1000

1200

1400

1600

1800

2000

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

Time of Day

Flow

(veh

/hr)

Low Wind Speed High Wind Speed

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Conclusions We observed traffic changes with rain at

these locations; amount varied with intensity and hour of daySpeeds 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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Conclusions We observed traffic changes with

visibility at these locations; amount varied with hour of daySpeeds up to 5 mph lower with low

visibilityFlows 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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Conclusions We observed traffic changes with wind

speed at these locations; amount varied with intensity and hour of daySpeeds up to 6 mph lower with high

windsFlows 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 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?

Thank you!