An Examination of “Fault,” “Unsafe Driving Acts” and “Total Harm” in Car-Truck Collisions

1. An Examination of “Fault,” “Unsafe Driving Acts” and “Total Harm” in Car-Truck Collisions Forrest Council (HSRC) David Harkey (HSRC) Daniel Nabors (BMI) Asad Khattak (UNC) Yusuf Mohamedshah (LENDIS) Sponsored By FHWA Highway Safety Information System (HSIS)

2. Study Goals • Further exploration of crashes involving one large truck and one car • Examination of “fault” in full-distribution of car/truck crashes (rather than just fatals) • Crash-based verification of “Unsafe Driving Acts (UDAs)” based on past data and expert judgment • ID “critical combinations” of roadway facilities and locations based on “total harm” – frequency + severity Highway Safety Information System (HSIS)

3. Past Findings • Truck/car crashes are severe, with non-truck occupants much more likely to be the one killed or injured • “High profile,” with much current emphasis on reducing truck-related fatalities (e.g., by 50% by 2009) • Car drivers are much more likely “at fault” in fatal car/truck crashes • Contributor in 81% and only contributor in 70% • “Fault” is less clear in studies of total car/truck crashes Highway Safety Information System (HSIS)

4. Past Findings (cont) • Based on expert-panel, top 12 of 26 UDAs for cars are: • Driving inattentively • Merging improperly, causing a truck to maneuver or brake quickly. • Failure to stop for a stop sign or light • Failure to slow down in a construction zone. • Unsafe speed (e.g., approaching from rear too fast) • Following too closely. • Failure to slow down for poor environmental conditions • Changing lanes abruptly in front of a truck. • Driving in the Ano zones@ • 3-way tie: • Unsafe turning, primarily turning with insufficient headway • Unsafe passing, primarily passing with insufficient headway • Pulling into traffic from roadside in front of truck without accelerating sufficiently. Highway Safety Information System (HSIS)

5. Past Findings (cont) • A second FARS-based UDA study says: • Car/truck crash-maneuvers are not much different from car/car maneuvers • Only 4 of 94 pre-crash maneuvers were more likely in car/truck crashes • Following improperly • Driving while drowsy or fatigued • Improper lane changing • Driving with vision obscured by rain, snow, fog, or dust. • But these were found in only 5% of fatal car/truck crashes Highway Safety Information System (HSIS)

6. Summary of Gaps • While cars are more “at fault” in fatal crashes, little data on non-fatal crashes • UDAs based on expert judgment need more crash-based validation • No study associating critical crash types or maneuvers with specific roadway characteristics (for treatment ID) Highway Safety Information System (HSIS)

7. Databases Used • “Fault” analysis for total car/truck crashes • 1994-97 NC data, where a contributing factor was assigned in 97% of the cases (as opposed to 1/3 of cases in GES files) • UDA verification • 1999 GES data • Roadway characteristics • 1994-97 NC crash and roadway inventory data Highway Safety Information System (HSIS)

8. Study Methods – “Fault” Analysis • “Fault” assigned to car or truck drivers if any contributing factor assigned by police • Analysis of car/truck cases with “fault” for • Non-truck only • Truck only • Both • Neither • Compare to earlier fatal-crash results Highway Safety Information System (HSIS)

9. Results – “Fault” Analysis • Overall, trucks more likely to be “contributing” than cars – 48% vs. 39% • Trucks more “at fault” in following crashes • Backing, rear-end crashes, right-turn (non-crossing), left-turn (non-crossing), sideswipe • Cars more “at fault” in • Head-on, angle, right-turn crossing • Differs from fatal-only findings somewhat Highway Safety Information System (HSIS)

10. Study Methods – UDA Verification • Could match 13 of 26 UDAs from expert panel with subsets of GES crash data • Ranked separately on frequency and severity of crash • Compared combined rank to “Top 12” from expert panel Highway Safety Information System (HSIS)

11. Results – UDA Analyses • Could only define GES crash subsets to “match” 13 of 26 UDAs (6 of “Top 12”) • Could not define #1 – “inattention” • For those matched, subsets were only small part of total car/truck crash problem • For three of “top 12” – 2% to 5% of problem • For other three of “top 12” – less than 1% of problem • Severity for these six was higher than for average car/truck crash. (Panel influenced more by severity?) Highway Safety Information System (HSIS)

12. Results – UDAs (cont) • 13 then ranked based on both frequency and severity • Combined ranking was sum of two ranks • Some general agreement with past rankings • Unsafe speed, failure to slow for poor weather, changing lanes abruptly • But some significant disagreements • Driving left of center #1 here, but not in “top 12” • Failure to slow in construction zone #4 by panel but #13 (last) in these rankings Highway Safety Information System (HSIS)

13. Study Methods – Critical Roadway Combinations • Assigned a “harm cost” to each car and truck based on severity level (fatal, injury, PDO) and thus to each crash • “Harm cost” based on comprehensive cost guidance from NHTSA and OST • Categorized crashes by 11 facility types (e.g., rural interstate), 7 crash types (e.g., head-on) and 6 location types (e.g., driveway, signalized intersection) • Calculated average “total harm cost” for each combination using regression model (to smooth the data) • Calculated “total harm cost” by multiplying by frequency Highway Safety Information System (HSIS)

14. Results – Critical Combinations • 325 NC combinations had sufficient data for “total harm” calculation • Top combination -- angle crashes at stop/yield intersections on undivided rural minor arterials and major collectors • Second – “angle” crashes on urban interstates (e.g., collision during passing or merging) • “Top” facility types – undivided rural minor arterials and major collectors, undivided rural principal arterials (i.e., interstates lower) • Top group included some high severity/low frequency (e.g., head-on) and some low-severity/high-frequency (e.g., rear-ends), supporting use of “total harm” analysis Highway Safety Information System (HSIS)

15. Summary • Cars are clearly not as “at fault” in total crashes, meaning that trucks should be targeted for intervention also • UDAs rankings by expert panels do not agree well with rankings based on crashes. If used for treatment development and targeting, better methods than expert rankings are needed. • “Total harm” can successfully be used to identify critical crash and roadway combinations, and would appear to be a feasible treatment targeting method. Highway Safety Information System (HSIS)