Predictors of alcohol impairment among crash involved drivers and riders in Western Australia

Transcription

1 Predictors of alcohol impairment among crash involved drivers and riders in Western Australia Peter Palamara Curtin-Monash Accident Research Centre School of Public Health, Curtin University Abstract Impairment due to alcohol continues to be a significant cause of traffic crashes and associated injury. In Western Australia 2010, around one-third of drivers/riders in fatal crashes recorded a Blood Alcohol Concentration level of 0.05g/100ml or higher. Understanding the risk factors for driver/rider impairment remains critical to establishing relevant and effective countermeasures. The aims of the study were to investigate various factors associated with reported BAC levels for motor car drivers and motorcycle riders involved in a crash in Western Australia during the period , and, to make relevant recommendations for policy and practice in managing the risk of alcohol impairment. Police reported crashes in Western Australia for the period were extracted from the Integrated Road Information System. Multinomial logistic regression was used to identify the road user factors significantly associated with a driver/rider recorded BAC of g/100ml; g/100ml and 0.101g/100ml compared with zero BAC (reference group). Valid data for the period was available for n=25,653 crash involved drivers/riders. Compared with drivers/riders with a BAC level of zero, the odds of recording a higher level BAC was significantly greater for those who were younger, male, unlicensed, and not wearing a seatbelt. Location of crash (remote area) was only significant at the highest level of BAC. The findings highlight the need for interventions that target at risk drivers and address the relationship between drink driving and other on-road risk behaviours. Background Alcohol is a highly researched, well-known cause of impairment for drivers and riders of motorised vehicles. It adversely affects reaction time, vision and judgment (WHO, 2007), thus significantly increasing the risk of a crash and the likelihood of death or serious injury in the event of a crash (Peden et al., 2004) even at Blood Alcohol Concentration levels as low as 0.04g/dl (Moskowitz & Fiorentino, 2000). For this reason the Blood Alcohol Concentration level for drivers and riders is typically restricted to 0.05g/dl for full licence holders and 0.00g/dl for novices (WHO, 2009). In Australia, alcohol is thought to account for 30% of fatal and 9% of serious injury crashes (ATC, 2011). These proportions were similarly noted in Western Australia in 2010 were around a third of fatal crashes and 10% of serious injury crashes were reported to be attributed to alcohol (Hill, Thompson, Yano & Smith, 2012). Epidemiological investigations of crashes involving alcohol have identified a number of significant driver related predictors and associated on-road behaviours. First and foremost, males are significantly more likely than females to be affected by alcohol at the time of a crash (see Palamara, Kaura & Fraser, 2013). In Western Australia for example, around 71% of all road users killed or hospitalised in an alcohol-related crash were male (Marchant et al., 2008). A likely contributing factor to this gender variation is the substantially higher level of alcohol consumption by males compared with females (Wilsnack, Wilsnack, Kristjanson & Vogeltanz-Holm, 2009). Second to gender, drivers involved in alcohol related crashes (greater than 0.00gm%) are more likely to be younger rather than older. In Western Australia, up to 50% of drivers aged years involved in a fatal crash in 2010 evidenced a Blood Alcohol Concentration greater than zero (Hill et al, 1

2 2012). The relatively high consumption of alcohol among younger age person (AIHW, 2008) plus their greater impairment at even low levels of alcohol relative to older age persons (Moskowitz & Fiorentino, 2000) increases their risk of crashing when having consumed alcohol. Other evidence shows that the burden of road crash related injury associated with drink driving is disproportionately high in rural areas of Australia (Havard, Shakeshaft, Conigrave, & Sanson-Fisher, 2011). In 2008, 54% of alcohol-related road fatalities occurred on country roads (Miller, Coomber, Zinkiewicz, & Toumbourou, 2010). In WA in 2006, 48% of alcoholrelated road fatalities and hospitalisations occurred in highly accessible areas, 8% in moderately accessible areas and 15% in remote and very remote areas (Marchant et al., 2008). It is clear that remote and very remote areas were over-represented in alcohol-related crashes as the population of these areas is very low. In recent review of alcohol related crashes and location of occurrence, Palamara et al (2013) suggested that the relatively high alcohol consumption by individuals who live in rural and remote areas (Parliament of Victoria Road Safety Committee, 2005) plus the lack of alternative transport options in these locations most likely increases the incidence of drink driving in these areas by local residents. Lastly, there is evidence to suggest that drink-driving does not occur in isolation of other onroad risk behaviours such as failing to wear a seat belt (WHO, 2007; Oxley et al, 2009). It is possible that alcohol affected drivers make poor choices in relation to belt use; it is also possible that the factors that predispose drivers to drink and drive also predispose them to not wear a seat belt independent of the influence of alcohol. Aims The aims of the study were to investigate various factors associated with police reported BAC levels for drivers and riders involved in a crash in Western Australia during the period , and, to make relevant recommendations for policy and practice in managing the risk of alcohol impairment. Methods Data retrieval and management Police records of all on-road motor vehicle crashes (both police attended/reported and road user reported) occurring during the period in Western Australia were extracted by Main Roads Western Australia from their Integrated Road Information System (IRIS). The data was imported to SPSS (Version 21) for management and analysis. After an initial set of analyses the larger dataset of crashes was reduced to those involving drivers of passenger cars, buses and trucks and riders of motorcycles and mopeds aged 17+ years for whom a Blood Alcohol Concentration (BAC) level was recorded. This procedure resulted in the identification of BAC level information for n=31,908 crashing drivers/riders. Data analysis The outcome variable for this investigation was driver/rider BAC level. Individual BAC levels were aggregated into the following four groups for analysis: 0.00gm/100ml; g/100ml; g/100ml and 0.101g/100ml. Categorical predictor variables of interest were driver/rider sex (male, female); age (17-19, 20-24, 25-39, 40-49, and 60+ years); licence type (valid licence, no valid licence); use of seat belt/helmet (use, non-use), and location of crash (metropolitan Perth, regional Western Australia, remote Western Australia) as a proxy for residential location. Univariate statistics were undertaken to describe the frequency distribution of the outcome and predictor variables and their association. Multivariate analysis of the relationship between predictor variables and driver/rider BAC levels was initially undertaken using Ordinal Logistic Regression because of the ordinal 2

3 nature of the dependent variable. However, after reviewing the goodness of fit and test of parallelism statistics this technique was rejected because the data did not support the required assumption of regression coefficients being equal for all categories of the outcome variable (Norusis, 2008). Alternatively, Multinomial Regression was undertaken; a technique which estimates coefficients for each outcome category. Results Descriptive statistics Table 1 presents the frequency distribution of relevant driver/rider crash variables. Around eight in ten crashing drivers/riders were reported by police to have a zero BAC level. Table 1: Frequency distribution of crashing driver/rider variables; WA Variable n % Blood Alcohol Concentration Level (gm%) 31, , , , , Vehicle type 31, Passenger vehicle 28, Motorcycle/moped 1, Bus/truck 1, Sex 31, Male 21, Female 10, Age (years) 31, , , , ,517 14, , , Licence type 30, Valid 27, No valid licence 2, Seat belt/helmet use 26, Used 26, Not used Location of crash (proxy for residence) 31, Metropolitan Perth 23, Regional Western Australia 5, Remote Western Australia 3,

4 A further 3.2% of drivers/riders presented with a BAC level greater than zero but below 0.05gm%, the legal limit for full licence holders. The remaining 16.5% of crashing drivers/riders presented with an illegal BAC, with the majority exceeding 0.100gm%. Most vehicle controllers were drivers of passenger vehicles (90.8%), male (67.5%), aged years, (31.3%), holding a valid licence (92.3%), reportedly used a seat belt or helmet at the time of the crash (97.5%) and crashed in the Perth metropolitan area the proxy for metropolitan residential location (73.1%). At the univariate level driver/rider BAC level was found to be significantly associated with vehicle type (X 2 = df=6; p 0.001), sex (X 2 = df=3; p 0.001), age (X 2 = df=15; p.001), licence type (X 2 = df=3; p 0.001), seat belt/helmet use (X 2 = df=3; p 0.001), and location of crash (X 2 =69.62 df=6; p 0.001). Drivers of buses/trucks, female drivers/riders, older age drivers, licensed drivers, users of seat belts/helmets, and drivers crashing/residing in metropolitan Perth were all significantly more likely to record a low legal or zero BAC level. Multivariate analysis The findings of the multivariate analysis of the data using Multinomial Regression are presented in Table 2 (over page). The appropriateness of the use of this procedure was confirmed by the significant statistics for the Likelihood Ratio Tests for the final model and the effect of the six selected driver/rider crash variables on driver/rider BAC level category. A BAC level of 0.00gm% was selected as the reference level. This analysis was based on complete data for n=25,264 drivers/riders, representing 79% of drivers/riders with a reported BAC level. In relation to driver sex, males were consistently twice as likely as female drivers/riders to record a higher level BAC. For driver/rider age, increased odds of returning a higher BAC level at all levels - were consistently noted for those aged between 17 and 39 years of age, while increased odds of a BAC of gm% and gm% were noted for drivers/riders aged between 40 and 59 years. Unlicensed drivers/riders also showed consistently greater odds than licensed drivers of returning a higher level BAC, with the odds progressively increasing for higher BAC levels, ranging from OR=2.72 for a BAC of gm% to OR=4.53 for gm%. A similar pattern of increasing odds with increasing BAC level was noted for drivers/riders who failed to use a seat belt or helmet, ranging from OR=2.53 for a BAC of gm% to OR=4.16 for a BAC of Compared with drivers of buses and trucks, drivers of passenger vehicles and riders of motorcycles/mopeds had consistently higher odds of returning a higher level BAC, with drivers evidencing higher odds than riders at each BAC level. Unlike the preceding variables, location of crash, the proxy for residential location, was not consistently associated with higher BAC levels. At the lowest positive level of BAC ( gm%), increased odds (OR=1.22) were noted only for drivers/riders crashing/residing in regional areas of Western Australia, while drivers/riders crashing/residing in remote (OR=1.32) and regional (OR=1.21) areas of Western Australia showed greater odds of returning a BAC 0.101gm%. 4

5 Table 2 Multinomial Logistic Regression of crashing driver/rider BAC level * ; WA Variable Blood Alcohol Concentration Level (gm%) OR 95%CI P value OR 95%CI P value OR 95%CI P value Sex Female^ Male Age (years) 60+^ ns ns Licence type Valid^ No valid licence Seat belt/helmet use Used^ Not used Vehicle type Bus/truck^ Passenger vehicle Motorcycle/moped Location of crash (proxy for residence) Metropolitan Perth^ Remote Western Australia ns ns Regional Western Australia ns *Reference category: BAC level 0.00gm%. ^ Reference value. -2 Log Likelihood=1.732E3 2 =2.876E3, df=36, p<

6 Discussion and conclusions This investigation has shown that around two in ten drivers/riders in Western Australia during the period crashed with a BAC level greater than zero and that most (10.5%) presented with a BAC greater than 0.100gm% double the legal limit in Western Australia. Second to this, the research noted that a number of driver/rider variables were independently associated with the likelihood of crashing with a BAC greater than zero. The finding that males were twice as likely as females to record a higher BAC at all three levels is consistent with previous research that has identified males as being more likely to crash while impaired by alcohol and serves to again underscore the relatively greater disposition of male drivers/riders to engage in aberrant, risky behaviour on the road. Similarly, the increased odds of younger age drivers, particularly those aged years, to drive and subsequently crash with illegal levels of BAC, highlights a contributing factor to well-known increased crash risk among this age group. It also highlights the need to address the high level of alcohol consumption among this group which contributes to the increased likelihood of drink-driving. The association of unlicensed driving and non-use of seat belt/helmet with increasing driver/rider BAC level supports the contention that aberrant risky driving behaviours can be part of a syndrome of on-road risk behaviours and may share a common antecedent. As such, interventions should adopt a common solutions approach rather than targeting problem driver behaviours in isolation of others. The findings also highlight the relatively low level of positive BAC among presumably professional drivers, that is drivers of buses and trucks for whom a zero BAC level would normally apply. Fewer than 3% of drivers of buses and trucks recorded a BAC greater than zero, while drivers of passenger vehicles and riders of motorcycles and mopeds were respectively 12 to seven times more likely than professional drivers to record BAC levels in excess of 0.100gm%. Finally, there was inconsistent evidence to conclude that drivers/riders crashing in nonmetropolitan areas, and presumably residing in those areas, are significantly more likely to be affected by alcohol at the time of a crash. The noted exception to this was for the highest level of BAC: compared with metropolitan drivers/riders, remote and regional drivers/riders were 30% to 20% more likely to crash with a BAC 0.101gm%. This could be due to a number of factors in these areas, including more relaxed community attitudes towards drinking and driving, a lack of alternative transport options, and a low risk of enforcement and detection real or perceived for drink-drivers/riders in these areas. The findings of this study have shown that the BAC of crashing drivers/riders is influenced by or associated with a number of factors. The results suggest that the high priority targets for drink-driving countermeasures include males and drivers/riders aged years. Somewhat less so, closer consideration should be given to the factors that increase the likelihood that drivers/riders in regional and remote Western Australia will drive and crash with significantly high levels of BAC. Lastly, countermeasures should acknowledge the identified relationship among driver/rider risk behaviours such as drink-driving, unlicensed driving and non-use of seat belts/helmets and target the common causes to these co-related behaviours. 6

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