John M. Sullivan. Truck Talk Truck Talk May 19, 2010

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1 The Nighttime Visibility ibilit of Trucks John M. Sullivan Truck Talk Truck Talk May 19, 2010

2 Nighttime Crash Risk and Rear-End Collisions 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, & 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 Craft (2005). Ayers et al. (1995) dispute conspicuity as a factor, citing alcohol and fatigue as primary causes.

3 Example Analysis: Fatal Rear-End Crashes with Trucks 70% Fatal Rear End Crash by Light Conditions ( ) 65.5% Percent 60% Daylight 50% Dawn/Dusk Dark/Dark w. Lights 40% Unknown 30% 20% 31.3% 10% 0% Truck Struck Crash Type 3.2% 0.1% Truck Striking Figure adapted from Craft, 2005

4 Fatal Rear-End Crashes with Trucks Nearly half occur at Less than 1/3 occur night Fatal Rear End Crash by Light Conditions ( ) at night Percent 70% 65.5% Daylight 60% Dawn/Dusk 48.3% 50% 46.3% Dark/Dark w. Lights 40% 30% 20% Unknown 31.3% 10% 0% 5.3% Truck Struck 3.2% 0.0% 0.1% Crash Type Truck Striking Figure adapted from Craft, 2005

5 Possible Factors Visibility Fatigue Alcohol Demographic differences

6 One Solution: Conspicuity Enhancement Assumes that: Drivers fail to see trucks on the roadway Fatal collisions often show no evidence of slowing down Addition of reflectors ecto will improve conspicuity cu Drivers will see trucks earlier and have more time to react Modified FMVSS-108 regulations: All heavy trailers manufactured after Dec 1,1993 require reflectors All tractors reflectorized by July 1, 1997 All trailers in the active fleet reflectorized by June 1, 2001

7 FMVSS-108 Reflectorization

8 Is there sufficient evidence that nighttime risk is related to visibility? No adjustment for Dark/Light exposure levels. Differences in day/night driver fatigue? Differences in day/night alcohol use? Demographic differences? (e.g., aggressive young male drivers) Could it be better or worse than implied?

9 Untangling darkness from other effects on crash risk Simple dark/light or day/night comparisons Other confounds: Traffic Density Seasonal Variation Winter is darker than Summer Demographic Changes Driver alertness Driver use of alcohol Daylight Saving Time comparisons: Based on analysis of same time of day, before and after clock change Assumes little variation in traffic density, driver demographics, alertness, alcohol use, or weather across dark and light intervals

10 Annual Solar Cycle (End of Civil Twilight) Time of Day 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 DST Transitions AM PM 0:00 1/1 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

11 Civil Twilight (Fall PM) 5:00 PM 6:00 PM 7:00 PM Light Dark 8:00 PM 9:00 PM Weeks before/after return to Standard Time

12 United States Counties Clock time of civil twilight end is tied to geographical location Tagged all crashes that fell into time window based on county latitude and longitude Determined 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), ]

13 Fatal Crash Types Most Affected by Light Level tio Da ark/light Ra Crash Type

14 What is the unconfounded effect of darkness on struck trucks? DST Analysis of fatal rear-end end collisions involving light vehicles and trucks Light vehicles = passenger cars, light trucks, minivans, SUVs Trucks = medium and heavy single-unit trucks and tractor-trailer t t combinations FARS

15 Fatal Rear-End Collisions by Vehicle and Light Condition Comparative Risk (Odds Ratio): Light Vehicle vs. Truck = % 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 39% 61% Light Vehicle Struck Crash Type 12% 88% Truck Struck Light Dark

16 Does Driver Age Play a Role? Older drivers have diminished contrast sensitivity and have special difficulty seeing at night. Is there an elevated crash risk among older drivers? Perhaps fatal rear-end collisions with trucks are insensitive to age differences?

17 Results Dark k/light Odd ds Truck Light Vehicle Driver Age

18 Results Age Age of driver increases dark/light odds ratio: 1.02 times each year of increasing age Odds of striking a truck at night is similar across age range ~4.5 times odds of striking a light vehicle Consistent with hypothesis that visibility is one factor contributing to risk in darkness.

19 Have conspicuity regulations solved the problem? Reported reduction of 43% in nighttime rear impacts into trucks (Morgan, 2001). New regulations should affect truck risk more than light vehicle risk Analysis examine fatal rear-end end collision across the pre- and post-regulation time period.

20 Conspicuity Analysis (DST Data) Dark/light ratios among earlier ( ) crashes were compared to later crashes ( ). 12/1/1993 New trailers fitted 6/1/1999-6/1/2001 Phase in 1/1/ /31/2003 Retrofit Trailers 6/1/1999 Split Dataset 1/1/1996

21 Results 100% 92/ /180 42/47 35/41 crashes in darkness s 75% 50% Percent 25% 0% Light Vehicle ( ) Light Vehicle ( ) Truck ( ) Truck ( ) Struck Vehicle by Time Period

22 Results - Conspicuity A significant decrease in dark/light odds was observed for BOTH light vehicles and trucks: But light vehicles are NOT subject to conspicuity regulations No interaction was observed between time period and vehicle type: The dark/light odds for trucks were not any more affected by time period than for light vehicles

23 Conclusions Risk of fatal rear-end end collisions in darkness is 4.5 times for trucks than for passenger cars. Risk 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.

24 Thank you.

Understanding Traffic Data: How To Avoid Making the Wrong Turn

Traffic Records Forum 2011 Understanding Traffic Data: How To Avoid Making the Wrong Turn Presenter: Marc Starnes (202) 366-2186 marc.starnes@dot.gov August 3rd, 2011 1 Summary of Topics Police Crash Reports