Odds of culpability associated with use of impairing drugs in injured drivers in Victoria, Australia

https://doi.org/10.1016/j.aap.2019.105389Get rights and content

Highlights

  • Culpability analysis was conducted on 5000 injured drivers in whom drug testing was conducted.

  • Alcohol gave large increases in the odds of culpability that was concentration-dependent.

  • Methylamphetamine also showed a large increase in the odds of culpability.

  • THC gave a modest increase in the odds of culpability

  • Benzodiazepines also gave a modest increase in the odds of culpability.

Abstract

Culpability analysis was conducted on 5000 drivers injured as a result of a vehicular collision and in whom comprehensive toxicology testing in blood was conducted. The sample included 1000 drivers for each of 5 years from approximately 5000–6000 drivers injured and taken to hospital in the State of Victoria. Logistic regression was used to investigate differences in the odds of culpability associated with alcohol and drug use and other selected crash attributes using the drug-free driver as the reference group. Adjusted odds ratios were obtained from multivariable logistic regression models in which other potentially explanatory driver and crash attributes were included. Drivers with alcohol present showed large increases in the odds of culpability similar to that seen in other studies investigating associations between blood alcohol concentration and crash risk. Methylamphetamine also showed a large increase in the odds of culpability (OR 19) compared to the reference group at both below and above 0.1 mg/L, whereas those drivers with Δ9-tetrahydrocannabinol (THC) present showed only modest increase in odds when all concentrations were assessed (OR 1.9, 95 %CI 1.2–3.1). Benzodiazepines in drivers also gave an increase in odds (3.2, 95 %CI 1.6–6.1), but not other medicinal drugs such as antidepressants, antipsychotics and opioids. Drivers that had combinations of impairing drugs generally gave a large increase in odds, particularly combinations of alcohol with THC or benzodiazepines, and those drivers using both THC and methamphetamine.

Introduction

Drugs capable of impairing key functions required for safe driving of motorized vehicles are one of several factors that increase crash risk. Globally, it is estimated that in 2013 there were over 188,000 alcohol-related road traffic deaths and a further almost 40,000 drug-related road traffic deaths (Poznyak, 2016). Drug use by drivers in the State of Victoria, Australia is also prevalent in both injured and killed drivers (Drummer et al., 2012, 2003; Di Rago et al., 2019b).

It is well recognized that around the world the drugs most capable of causing impairment, after alcohol, are illicit substances, particularly amphetamines, cannabis, and cocaine, although opioids and benzodiazepines are commonly associated with traffic injuries and death, and often in combination with other substances, including to some degree the novel psychoactive substances (NPS) (Gadegbeku et al., 2011; Movig et al., 2004; Li et al., 2013; Legrand et al., 2012; Bernhoft et al., 2012; Morland et al., 2011).

While there is little dispute that most of the drugs used recreationally can cause significant reduction in cognitive and psychomotor functions there is still some doubt over the extent that these drugs affect crash risk. Estimates of crash risk arise from three main types of analyses; i) by estimating the prevalence of specific drugs or drug classes in drivers that have crashed compared to drivers that have not had a collision (Movig et al., 2004; Mura et al., 2003; Hels et al., 2013), ii) from culpability analyses (sometimes called responsibility analyses) where the proportion of culpable drivers using a particular drug is compared to the proportion of drivers not using drugs (Gadegbeku et al., 2011; Drummer et al., 2004; Poulsen et al., 2014; de Carvalho et al., 2016; Dubois et al., 2015; Reguly et al., 2014; Laumon et al., 2005) and iii) from data obtained from population databases and registries (Dischinger et al., 2011; Corsenac et al., 2012; Leveille et al., 1994; Meuleners et al., 2011; Monarrez-Espino et al., 2016).

Meta-analyses of published studies generally show increases in crash risk, particularly for users of amphetamines (e.g. methylamphetamine and amphetamine) and cocaine (Elvik, 2013). The presence of THC in blood shows a more modest increase in crash risk with estimates (as odds ratios, OR) ranging from not significant to over 2, with most OR showing a less than doubling when adjusted for possible confounders (Gadegbeku et al., 2011; Li et al., 2013; Bernhoft et al., 2012; Hels et al., 2013; Drummer et al., 2004; Poulsen et al., 2014; Elvik, 2013; Martin et al., 2017; Asbridge et al., 2012). Crash risks for benzodiazepines and opioids are not so well established given both their prescribed and recreational use. Meta-analyses of published studies that include case control design, crash involvement or from determination of crash culpability show variable crash risk for these two classes (Elvik, 2013; Chihuri and Li, 2017; Dassanayake et al., 2011).

Culpability analysis has been used in several studies as originally reported (Robertson and Drummer, 1994) or with some variations in a number of subsequent studies (Gadegbeku et al., 2011; Drummer et al., 2004; Poulsen et al., 2014; Laumon et al., 2005; Brubacher et al., 2019; Longo et al., 2000). This has allowed an assessment of any changes to the proportion of culpable drivers within a number of categories including the effect of alcohol and various drugs summarized as an OR using the drug-free driver as the reference group. Changes in the OR may provide an estimate of the effect of drugs on crash risk providing any confounding factors can be accommodated in multivariate statistical calculations.

In the state of Victoria, the presence of methylamphetamine (MA), 3,4-methylenedioxy-methylamphetamine (MDMA) and Δ9-tetrahydrocannabinol (THC) has been prohibited in drivers of motorized vehicles. Since mid 2009 Victoria has legislated compulsory drug testing of all drivers hospitalized as a result of a road traffic collision. Approximately 5000–6000 blood specimens are analyzed at the Victorian Institute of Forensic Medicine annually for alcohol (ethanol), THC, MA and MDMA in accordance with the Victorian Road Safety Act (1986).

Blood specimens collected following a collision under the Victorian Injured Driver Drug Testing Program provide an excellent ongoing opportunity to add to the body of evidence surrounding drug use trends and insight to crash-risk among Victorian drivers through use of culpability analysis.

This study estimates the odds of culpability of drivers with detected drugs in Victorian injured-drivers hospitalized over the 5-year period to mid 2018 using a previously validated culpability method of determining driver contribution to a crash.

Section snippets

General

A blood specimen was taken from each driver admitted to a Victorian hospital (includes attendance at emergency units at hospitals) as a result of a road traffic crash as part of the State’s legislative requirements. Blood was collected by a medical practitioner or registered nurse at each hospital as soon as practicable after admission, and placed in sample tubes containing preservative (1 % sodium fluoride/potassium oxalate).

As part of this project 1000 drivers from each of the 5-year periods

Results and discussion

Of the 5000 cases analyzed 12 were subsequently excluded since they were later found not to be drivers. This left 4988 drivers, of which 63.1 % were positive to alcohol and/or one of the detected drugs. Details of the presence of these drugs in injured drivers have been detailed elsewhere (Di Rago et al., 2019b).

Both age and gender affected the odds of being responsible among drivers injured in a crash (Drummer et al., 2004; Chihuri and Li, 2019) (Table 1). Drivers aged between 40 and 59 years

Conclusion

This culpability analysis of almost 5000 injured drivers has provided further evidence of the elevated odds of culpability associated with alcohol and methylamphetamine using drivers as well as drivers positive to THC, particularly those with higher blood concentrations. Of all the legally-available drugs benzodiazepines used in isolation show a modest increase in culpability but are most often associated with other potentially impairing drugs.

Submission declaration and verification

This manuscript has not been published previously (except in the form of an abstract, or lecture), and it is not under consideration for publication elsewhere. This publication is approved by all authors and explicitly by the responsible authorities where the work was carried out, and that, if accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder

Author contributions

Dimitri Gerostamoulos: Substantial contribution to the study conception and design, data acquisition, supervision of analyses and interpretation, drafting or revising the article for intellectual content. Revision of the article for intellectual content, approval of the final version.

Matthew Di Rago: Analytical analyses, data acquisition and analysis, revision of the article for intellectual content, approval of the final version.

Noel W. Woodford: Contribution to the study conception and

Declaration of Competing Interest

None.

Acknowledgements

The authors gratefully acknowledge the support of the Department of Justice, VicRoads, the Transport Accident Scheme (TAC) and Victoria Police that formed the Road Safety Executive (Victoria) and funded the study. In particular, gratitude is extended to William Gibbons (Department of Justice) and Inspector Tom McGillian (Victoria Police) for their support. We also thank Gemma Wynd of the Road Policing Drug and Alcohol Section of Victoria Police who assisted with data entry and culpability

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