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Jaeyoung Lee, Ph.D Candidate
Dr. Mohamed Abdel-Aty, Ph.D
Dr. Mohamed Ahmed, Ph.D
Traffic Safety under Reduced Visibility 2
• Florida is among the top state in the US regarding traffic safety
problems resulting from adverse visibility conditions due to
fog/smoke and heavy rain.
Crashes due to Reduced Visibility
2,664
2,052
2,021
Texas
Fl
California
Number of Fatal Crashes due to Fog/Smoke/Rain in 2001-2010
Traffic Safety under Reduced Visibility 3
Pile-up Crash on I-75 in 2012
• Recently, 10 people were killed and another 18 were injured
from fog/smoke related pile-up crash on I-75 near Gainesville
(Jan 29, 2012).
Traffic Safety under Reduced Visibility 4
Severity of Visibility related Crashes
• Generally, Crashes due to reduced visibility from fog/smoke
are more severe compared to non-fog related crashes.
0%
10%
20%
30%
40%
50%
60%
PDOPossible Injury
Non-incapacitatingInjury
IncapacitatingInjury
Fatality
51%
24%
17%
7%
1%
42%
20%23%
10%
5%
Clear Vision
Fog or Smoke
Traffic Safety under Reduced Visibility 5
Temporal Distributions (1/4)
• Hourly distribution of fog crashes shows that early hours of
dawn & subsequent hours where fog is prominent (5-8 AM).
4% 4%6% 6%
5%
12%
23%
21%
6%
1%0% 0% 0% 0% 0% 0% 0% 0% 1% 1% 1%
2% 2% 2%
0%
5%
10%
15%
20%
25%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Cra
sh P
erc
ent
age
Military Hours (24h)
Fog
CVState Roads (2005-2010) in Florida
Traffic Safety under Reduced Visibility 6
Temporal Distributions (2/4)
• Hourly distribution of smoke crashes does not show any
obtrusive patterns, which implies smoke crashes do not occur
at specific time period.
2% 3% 3%2% 2% 2%
3%
10%
5%6%
5% 5%4%
7% 6%5%
4% 5% 5%
3%2%
5% 5%
3%
0%
5%
10%
15%
20%
25%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Cra
sh P
erc
enta
ge
Military Hours (24h)
Smoke
CVState Roads (2005-2010) in Florida
Traffic Safety under Reduced Visibility 7
Temporal Distributions (3/4)
• Monthly distribution of fog crashes indicated nearly 60% of
fog crashes occurs during the winter period, from Dec to Feb.
24%
14%
9%
5% 5%
2% 2% 2%2%
7%9%
20%
0%
5%
10%
15%
20%
25%
30%
1 2 3 4 5 6 7 8 9 10 11 12
Cra
sh P
erc
enta
ge
Month
Fog
CVState Roads (2005-2010) in Florida
Traffic Safety under Reduced Visibility 8
Temporal Distributions (4/4)
• Monthly distribution of smoke crashes showed it most
frequently occurs in May which is the dry period.
8% 8%6%
10%
25%
7%8%
4%
6%7%
5%
8%
0%
5%
10%
15%
20%
25%
30%
1 2 3 4 5 6 7 8 9 10 11 12
Cra
sh P
erc
enta
ge
Month
Smoke
CVState Roads (2005-2010) in Florida
Traffic Safety under Reduced Visibility 9
Spatial Distributions (1/3)
• Kernel density estimation was used to identify fog/smoke
crash hotspots.
Cluster County Cluster County
1 Pinellas, Hillsborough & Pasco 7 Miami-Dade & Broward
2 Polk & Osceola 8 Lee & Charlotte
3 Duval 9 Glades & Hendry
4 Leon 10 Bay
5 Alachua 11 Brevard & Orange
6 Orange
Traffic Safety under Reduced Visibility 10
Hotspot Identification in Florida
Traffic Safety under Reduced Visibility 10
Traffic Safety under Reduced Visibility 11
Spatial Distributions (2/3)
• 11 hotspots were magnified and divided highways into one
mile segments and thus FS crashes were counted based on the
segments.
Traffic Safety under Reduced Visibility 12
Spatial Distributions (3/3)
• Segment 2 on I-75 were identified as a fog/smoke crash
hotspot using previous crash data (2005-2010), the pile-up
crash occurred due to fog & smoke involving large trucks at
the very same location.
• Thus, this crash could be avoided
if appropriate treatments were
conducted, proactively.
Traffic Safety under Reduced Visibility 13
Contributing Factors (1/3)
• Fog crashes are more frequent at the roadway with poor
lighting condition, divided median, and at segments (not
intersections) in the rural area.
0%
10%
20%
30%
40%
50%
60%
70%
DaylightDusk
DawnDark (street
lighting) Dark (nostreet
lighting)
24%
2%
18% 20%
36%
68%
2%1%
21%
7%
Fog
CV
Fog crashes by lighting conditions
Traffic Safety under Reduced Visibility 14
Contributing Factors (2/3)
0%
10%
20%
30%
40%
50%
60%
State HighwayLocal Roadway
54%
46%
59%
41%
0%
20%
40%
60%
80%
100%
UrbanRural
48% 52%
85%
15%
Fog
CV
0%
10%
20%
30%
40%
50%
60%
DividedUndivided
41%
59%55%
45%
0%10%20%30%40%50%60%
SegmentAt
intersection Influencedby
intersection
56%
39%
5%
45% 47%
8%
Fog crashes by roadway types Fog crashes by community types
Fog crashes by median types Fog crashes by locations
Traffic Safety under Reduced Visibility 15
Contributing Factors (3/3)
• Smoke crashes are more frequent at the roadway with poor
lighting condition, and at segments (not at intersections) in the
rural area.
0%
20%
40%
60%
80%
Daylight Dusk Dawn Dark (streetlighting)
Dark (no streetlighting)
57%
1% 7%15% 20%
68%
2% 1%
21%7%
Smoke
CV
0%
20%
40%
60%
80%
100%
Urban Rural
49% 51%
85%
15%
0%
20%
40%
60%
80%
Segment At intersection Influenced byintersection
70%
25%
5%
45% 47%
8%
Traffic Safety under Reduced Visibility 16
Frequent Crash Types in Fog Crashes
• Fog crashes lead to more severe injuries and are associated
with rear-end crashes compared to crashes in clear vision (CV)
conditions.
• Moreover, multivehicle, rear-end, head-on or angle crashes
occurring in foggy conditions have significantly higher
probability to result in severe crashes.
0.00 0.50 1.00 1.50 2.00 2.50
Severe injury
Rear-end
Severe injury × Multiple
Severe injury × Rear-end
Severe injury × Head-on
Severe injury × Angle
1.88
1.40
2.06
2.04
1.63
1.81
Odds ratio of crash types and their interactions in fog to CV crash
Traffic Safety under Reduced Visibility 17
Frequent Crash Types in Smoke Crashes
• Smoke crashes lead to more severe injury crashes and are
associated with multiple, rear-end and head-on crashes.
• In addition, multivehicle, rear-end or head-on or angle crashes
occurring in smoky conditions have higher probability to result
in severe crashes.
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Severe injury
Multiple vehicle
Rear-end
Head-on
Severe injury × Multiple vehicle
Severe injury × Rear-end
Severe injury × Head-on
1.21
1.10
1.15
1.03
2.99
1.64
1.07
Odds ratio of crash types and their interactions in smoke to CV crash
Traffic Safety under Reduced Visibility 18
Summary (1/3)
• Florida is among the top state in the US regarding traffic
safety problems resulting from adverse visibility conditions
due to fog/smoke and heavy rain.
• Crashes due to reduced visibility from fog/smoke are more
severe compared to non-fog related crashes.
• Fog crashes occur mostly in the morning in Dec to Feb,
whereas smoke related crashes occur most frequently in May.
Traffic Safety under Reduced Visibility 19
Summary (2/3)
• Roadway with poor lighting condition, undivided segments
(not at intersection) in the rural area has the increased
probability of fog/smoke crash occurrence.
• Through the macroscopic analysis, we can understand the big
picture of fog/smoke crashes, and more specific segments
with frequent fog/smoke crashes can be identified through
micro-level analysis.
Traffic Safety under Reduced Visibility 20
Summary (3/3)
• Both fog and smoke crashes lead to more severe injuries
compared to crashes in CV conditions.
• Furthermore, multivehicle, rear-end, head-on or angle crashes
occurring in foggy conditions have significantly higher
probability to result in severe crashes.
Jaeyoung Lee, Ph.D Candidate
Dr. Mohamed Abdel-Aty, Ph.D
Dr. Mohamed Ahmed, Ph.D
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