Th Ni htti Vi ibilit f T kTh Ni htti Vi ibilit f T kThe Nighttime Visibility of TrucksThe Nighttime Visibility of Trucks

John M. Sullivan

Truck TalkTruck TalkMay 19, 2010

Nighttime Crash Risk and RearNighttime Crash Risk and Rear--End End Collisions with TrucksCollisions with Trucks

67% fatal underrides occurred in darkness (Minahan(& O’Day, 1977)Normalized truck crashes by travel category suggests crash risk is higher at night (Campbell, Blower, Gatts, g g ( p , , ,& Wolfe, 1988)About 3 times fatalities per thousand crashes occur between midnight and 6 am (Blower & Campbell, 1998).

Non-truck-driver fatigue and alcohol use is implicated.Visibility and alcohol also cited in recent work by C ft (2005)Craft (2005).Ayers et al. (1995) dispute conspicuity as a factor, citing alcohol and fatigue as primary causes.

Example Analysis: Fatal RearExample Analysis: Fatal Rear--End End Crashes with TrucksCrashes with Trucks

65.5%

60%

70%Fatal Rear End Crash by Light Conditions (1994-1998)

Daylight

31.3%40%

50% Dawn/DuskDark/Dark w. LightsUnknown

Per

cent

10%

20%

30%P

3.2%0.1%

0%

10%

Truck Struck Truck StrikingCrash TypeCrash Type

Figure adapted from Craft, 2005

Fatal RearFatal Rear--End Crashes with TrucksEnd Crashes with TrucksFatal RearFatal Rear--End Crashes with TrucksEnd Crashes with Trucks

Nearly half occur at i ht

Less than 1/3 occur t i ht

65.5%

60%

70%Fatal Rear End Crash by Light Conditions (1994-1998)

DaylightDawn/Dusk

night at night

48.3% 46.3%

31.3%40%

50% Dark/Dark w. LightsUnknown

Per

cent

10%

20%

30%P

5.3% 3.2%0.0% 0.1%

0%

10%

Truck Struck Truck StrikingCrash TypeCrash Type

Figure adapted from Craft, 2005

Possible FactorsPossible FactorsPossible FactorsPossible Factors

VisibilityVisibilityFatigueAlcoholAlcoholDemographic differences

One Solution:One Solution:Conspicuity EnhancementConspicuity Enhancement

Assumes that:Assumes that:Drivers fail to see trucks on the roadway

• Fatal collisions often show no evidence of slowing downAddition of reflectors will improve conspicuitydd t o o e ecto s p o e co sp cu tyDrivers will see trucks earlier and have more time to react

Modified FMVSS-108 regulations:Modified FMVSS 108 regulations:All heavy trailers manufactured after Dec 1,1993 require reflectorsAll tractors reflectorized by July 1, 1997y y ,All trailers in the active fleet reflectorized by June 1, 2001

FMVSSFMVSS--108108 ReflectorizationReflectorizationFMVSSFMVSS--108 108 ReflectorizationReflectorization

Is there sufficient evidence that Is there sufficient evidence that nighttime risk is related to visibility?nighttime risk is related to visibility?

No adjustment for Dark/Light exposure levelsNo adjustment for Dark/Light exposure levels. Differences in day/night driver fatigue?Differences in day/night alcohol use?Differences in day/night alcohol use?Demographic differences? (e.g., aggressive young male drivers)young male drivers)Could it be better or worse than implied?

Untangling darkness from other effects Untangling darkness from other effects on crash riskon crash risk

Simple dark/light or day/night comparisonsSimple dark/light or day/night comparisonsOther confounds:

• Traffic Density• Seasonal Variation Winter is darker than Summer• Seasonal Variation—Winter is darker than Summer• Demographic Changes• Driver alertness• Driver use of alcohol• Driver use of alcohol

Daylight Saving Time comparisons:Based on analysis of same time of day, before and ft l k hafter clock change

Assumes little variation in traffic density, driver demographics, alertness, alcohol use, or weather

d k d li ht i t lacross dark and light intervals

Annual Solar CycleAnnual Solar CycleAnnual Solar CycleAnnual Solar Cycle(End of Civil Twilight)(End of Civil Twilight)

4:00

6:00

8:00 AM10:00

12:00

14:00e of

Day

AMPM

DST Transitions

16:00

18:00

20:00

Tim

e

22:00

0:001/1 1/31 3/2 4/1 5/1 5/31 6/30 7/30 8/29 9/28 10/28 11/27 12/27

Month/Day

Civil Twilight (Fall PM)Civil Twilight (Fall PM)

5:00 PM5:00 PM

6:00 PM

7:00 PMLight Dark

8:00 PM

9:00 PM9:00 PM-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9

Weeks before/after return to Standard Time

United States CountiesUnited States CountiesClock time of civil twilight end is tied to geographical locationgeographical location

Tagged all crashes that fell into time window based on county latitude and longitudeDetermined weeks relative to DST changeover from crash date

[For further detals refer to: Sullivan and Flannagan (2002)[For further detals refer to: Sullivan and Flannagan (2002). Accident Analysis and Prevention, 34(4), 487-498.]

Fatal Crash Types Most Affected by Fatal Crash Types Most Affected by Light LevelLight Level

10

7 8 9

tio

4 5 6

ark/

Ligh

t Ra

1 2 3 D

a

0

Crash Type

What is the What is the unconfoundedunconfounded effect of effect of darkness on struck trucks?darkness on struck trucks?

DST Analysis of fatal rear end collisionsDST Analysis of fatal rear-end collisions involving light vehicles and trucks

Light vehicles = passenger cars, light trucks,Light vehicles passenger cars, light trucks, minivans, SUVsTrucks = medium and heavy single-unit trucks and t t t il bi titractor-trailer combinations

FARS 1987-2003

Fatal RearFatal Rear--End Collisions by Vehicle End Collisions by Vehicle and Light Conditionand Light Condition

Comparative Risk (Odds Ratio):

88%

80%90%

100%LightDark

Light Vehicle vs. Truck = 4.5

39%

61%

50%60%70%

39%

12%20%30%40%

0%10%

Light Vehicle Struck Truck StruckCrash TypeCrash Type

Does Driver Age Play a Role?Does Driver Age Play a Role?Does Driver Age Play a Role?Does Driver Age Play a Role?

Older drivers have diminished contrastOlder drivers have diminished contrast sensitivity and have special difficulty seeing at night.gIs there an elevated crash risk among older drivers?Perhaps fatal rear-end collisions with trucks are insensitive to age differences?

ResultsResultsResultsResults

20

14

16

18

ds

8

10

12

k/Li

ght O

dd

TruckLi ht V hi l

2

4

6

8

Dar

k Light Vehicle

0

2

10 20 30 40 50 60 70 80Driver AgeDriver Age

ResultsResults –– AgeAgeResults Results –– AgeAge

Age of driver increases dark/light odds ratio:Age of driver increases dark/light odds ratio:1.02 times each year of increasing age

Odds of striking a truck at night is similarOdds of striking a truck at night is similar across age range

~4.5 times odds of striking a light vehicleg gConsistent with hypothesis that visibility is one factor contributing to risk in darkness.g

Have conspicuity regulations solved Have conspicuity regulations solved the problem?the problem?

Reported reduction of 43% in nighttime rearReported reduction of 43% in nighttime rear impacts into trucks (Morgan, 2001).New regulations should affect truck risk moreNew regulations should affect truck risk more than light vehicle riskAnalysis – examine fatal rear-end collisionAnalysis examine fatal rear end collision across the pre- and post-regulation time period.

ConspicuityConspicuity Analysis (DST Data)Analysis (DST Data)Conspicuity Conspicuity Analysis (DST Data)Analysis (DST Data)

Dark/light ratios among earlier (1987-1995) crashes were compared to later crashes (1996-2003)2003).

12/1/1993New trailers fitted

6/1/1999 - 6/1/2001Phase in

New trailers fitted

1/1/1987 12/31/2003

6/1/1999Retrofit Trailers

1/1/1996Split Dataset

ResultsResultsResultsResults

100%

s

92/130 106/180 42/47 35/41

75%

n da

rkne

ss

50%

cras

hes

in

0%

25%

Perc

ent

0%Light Vehicle(1987-1995)

Light Vehicle(1996-2003)

Truck(1987-1995)

Truck(1996-2003)

Struck Vehicle by Time Period

ResultsResults -- ConspicuityConspicuityResults Results -- ConspicuityConspicuity

A significant decrease in dark/light odds wasA significant decrease in dark/light odds was observed for BOTH light vehicles and trucks:

But…light vehicles are NOT subject to conspicuity l iregulations

No interaction was observed between time period and vehicle type:period and vehicle type:

The dark/light odds for trucks were not any more affected by time period than for light vehicles

ConclusionsConclusionsConclusionsConclusions

Risk of fatal rear end collisions in darkness isRisk of fatal rear-end collisions in darkness is 4.5 times for trucks than for passenger cars.Risk in darkness increases with the age of theRisk in darkness increases with the age of the striking driver for both light vehicle and truck collisions.

Suggests darkness and diminished contrast sensitivity compound the problem.

DST evidence of the effectiveness of conspicuity treatments is small.

Thank youThank youThank you.Thank you.