SWOV Catalogus

343582

Driver toxicology testing and the involvement of marijuana in fatal crashes, 2010-2014 : a descriptive report.
20170242 ST [electronic version only]

Olympia, WA, Washington Traffic Safety Commission, 2016, 56 p., 16 ref.

Samenvatting The Fatality Analysis Reporting System (FARS) contains significant limitations in analysing drug positive drivers involved in fatal crashes. Most notable to Washington, this data does not offer a cannabinoid code set that distinguishes between delta-9-THC and the metabolite, carboxy-THC. The levels of drugs present in blood are also not recorded in the FARS system, although they are provided in toxicology reports. In response to this limitation, Washington FARS Analysts, in collaboration with the State Toxicologist, manually abstracted cannabinoid drug results for deceased and surviving drivers involved in fatal crashes when toxicology analysis was performed. This report is a description of this newly compiled data. The following is a summary of key observations gleaned from this more detailed fatal crash information with a focus on cannabinoid-positive drivers: * From 2010-2014 there were 3,027 drivers involved in fatal crashes, of which 1,773 (58.6 percent) were tested for both alcohol and drugs with known results. Of the 1,773 drivers analysed 1,061 (59.8 percent) were positive for alcohol and/or drugs. * In 2014, 84.3 percent of drivers positive for cannabinoids were positive for THC, compared to only 44.4 percent of cannabinoid-positive drivers in 2010. In 2014, among the 75 drivers involved in fatal crashes positive for THC, approximately half (38) exceeded the 5 ng/ml THC per se limit. * The frequency of drivers in fatal crashes that tested positive for THC, alone or in combination with alcohol or other drugs, was highest in 2014 (75 drivers) compared to the previous four-year average (36 drivers). The frequency of drivers with alcohol greater than/equal to BAC .08 and no other drugs was lowest in 2014 (51 drivers) compared to the previous four-year average (98 drivers). * From the 1,061 drivers who tested positive for alcohol and/or drugs, mutually exclusive driver categories were established. This report focuses on a subset of these driver comparison groups (547 total drivers): - Only THC (56, 5.3 percent) - Only carboxy-THC (37, 3.5 percent) - THC and alcohol greater than/equal to BAC .08 (83, 7.8 percent) - THC, alcohol greater than/equal to BAC. 08, and drugs (18, 1.7 percent) - THC and other drugs (39, 3.7 percent) - Only alcohol greater than/equal to BAC .08 (314, 29.6 percent) * Among drivers in fatal crashes that tested positive for only THC or only carboxy-THC, the largest proportion are ages 16-25. This age group also had the highest proportion of drivers with alcohol greater than/equal to BAC .08. Of drivers that tested positive for the combination of THC and alcohol greater than/equal to BAC 0.08, 39.8 percent were ages 16-25. ?Similar to drivers with only alcohol greater than/equal to BAC .08, drivers with the combination of THC and alcohol greater than/equal to BAC .08 were involved in fatal crashes that occurred most frequently on the weekends. Drivers with only THC were involved in fatal crashes that occurred equally between weekends (48.2 percent) and weekdays (51.8 percent). * Drivers with alcohol greater than/equal to BAC .08, alone or in combination with other drugs, were involved in fatal crashes that occurred most often during the nighttime hours (6 p.m. – 5 a.m.). Drivers with only THC or only carboxy-THC were involved in fatal crashes that occurred most often during the daytime hours, similar to drivers with no drugs or alcohol. * Drivers with only alcohol greater than/equal to BAC .08 were involved in fatal crashes that occurred most frequently on rural roads (58.6 percent), whereas the majority of drivers with only THC were involved in fatal crashes that occurred most frequently on urban roads (58.9 percent). * Drivers with alcohol greater than/equal to BAC .08, alone or in combination with other drugs, were most frequently the only unit (no other vehicles or non-motorists) involved in the fatal crash. In contrast, over 70 percent of drivers with only THC or only carboxy-THC were involved in multiple unit fatal crashes, similar to the frequency of drivers with no drugs or alcohol. * Drivers involved in fatal crashes with no drugs or alcohol and drivers with only carboxy-THC had the highest frequency of no reported crash contributing circumstances (approximately 44 percent). Among drivers with only THC, 28.6 percent had no other crash contributing circumstances reported, compared to 17.5 percent of drivers with only alcohol greater than/equal to BAC .08. * The most frequently reported driver error among drivers in fatal crashes with only THC was lane deviation (12.5 percent), followed by overcorrecting (8.9 percent). * More than half of drivers with only alcohol greater than/equal to BAC .08 involved in fatal crashes were speeding. Over 60 percent of drivers with alcohol greater than/equal to BAC .08 and THC combined were speeding. The observations described in this report are insufficient for determining the link between THC and crash risk. The full limitations of this information as it is presented in this report are detailed in the following section. (Author/publisher)
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