1 the effects of weather on freeway traffic flow meead saberi k. priya chavan robert l. bertini...
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1
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.
2
Objectives
Precipitation
Visibility
Wind Speed
Speed
Flow
3
Study Area
I-5 NB Freeway
Portland, ORMP 302.5MP 305.12MP 307.9
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 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!
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