Limits of the quasi-induced exposure method when compared with the standard case-control design. Application to the estimation of risks associated with driving under the influence of cannabis or alcohol

Schizophrenia, antipsychotic treatment adherence and driver responsibility for motor vehicle crash: a population-based retrospective study in British Columbia, Canada

OBJECTIVE

To examine the relationship between schizophrenia, antipsychotic medication adherence and driver responsibility for motor vehicle crash.

DESIGN

Retrospective observational cohort study using 20 years of population-based administrative health and driving data.

SETTING

British Columbia, Canada.

PARTICIPANTS

Licensed drivers who were involved in a police-attended motor vehicle crash in British Columbia over a 17-year study interval (2000-16).

EXPOSURES

Incident schizophrenia was identified using hospitalisation and physician services data. Antipsychotic adherence was estimated using prescription fill data to calculate the 'medication possession ratio' (MPR) in the 30 days prior to crash.

PRIMARY OUTCOME MEASURES

We deemed drivers 'responsible' or 'non-responsible' for their crash by applying a validated scoring tool to police-reported crash data. We used logistic regression to evaluate the association between crash responsibility and exposures of interest.

RESULTS

Our cohort included 808 432 drivers involved in a police-attended crash and for whom crash responsibility could be established. In total, 1689 of the 2551 drivers with schizophrenia and 432 430 of the 805 881 drivers without schizophrenia were deemed responsible for their crash, corresponding to a significant association between schizophrenia and crash responsibility (66.2% vs 53.7%; adjusted OR (aOR), 1.67; 95% CI, 1.53 to 1.82; p<0.001). The magnitude of this association was modest relative to established crash risk factors (eg, learner license, age ≥65 years, impairment at time of crash). Among the 1833 drivers with schizophrenia, near-optimal antipsychotic adherence (MPR ≥0.8) in the 30 days prior to crash was not associated with lower crash responsibility (aOR, 1.04; 95% CI, 0.83 to 1.30; p=0.55).

CONCLUSIONS

Crash-involved drivers with schizophrenia are more likely to be responsible for their crash, but the magnitude of risk is similar to socially acceptable risk factors such as older age or possession of a learner license. Contemporary driving restrictions for individuals with schizophrenia appear to adequately mitigate road risks, suggesting more stringent driving restrictions are not warranted.

Syncope and Traffic Crash: A Population-Based Case-Crossover Analysis

BACKGROUND

Among individuals with recent syncope, recurrence of syncope while driving might incapacitate a driver and cause a motor vehicle crash. Current driving restrictions assume that some forms of syncope transiently increase crash risk. We evaluated whether syncope is associated with a transient increase in crash risk.

METHODS

We performed a case-crossover analysis of linked administrative health and driving data from British Columbia, Canada (2010 to 2015). We included licensed drivers who visited an emergency department with "syncope and collapse" and who were involved as a driver in an eligible motor vehicle crash, both within the study interval. Using conditional logistic regression, we compared the rate of emergency visits for syncope in the 28 days before crash (the "pre-crash interval") with the rate of emergency visits for syncope in 3 self-matched 28-day control intervals (ending 6, 12, and 18 months before the crash).

RESULTS

Among eligible crash-involved drivers, 47 of 3026 pre-crash intervals and 112 of 9078 control intervals had emergency visits for syncope, indicating syncope was not significantly associated with subsequent crash (1.6% vs 1.2%; adjusted odds ratio [OR], 1.27; 95% confidence interval [CI], 0.90-1.79; P = 0.18). There was no significant association between syncope and crash in subgroups at higher risk for adverse outcomes after syncope (eg, age > 65 years, cardiovascular disease, cardiac syncope).

CONCLUSIONS

In the context of prevailing modifications of driving behaviour after syncope, an emergency department visit for syncope did not transiently increase the risk of subsequent traffic collision. Overall crash risks after syncope appear to be adequately addressed by current driving restrictions.

Effectiveness of road safety interventions: An evidence and gap map

Background

Road Traffic injuries (RTI) are among the top ten leading causes of death in the world resulting in 1.35 million deaths every year, about 93% of which occur in low- and middle-income countries (LMICs). Despite several global resolutions to reduce traffic injuries, they have continued to grow in many countries. Many high-income countries have successfully reduced RTI by using a public health approach and implementing evidence-based interventions. As many LMICs develop their highway infrastructure, adopting a similar scientific approach towards road safety is crucial. The evidence also needs to be evaluated to assess external validity because measures that have worked in high-income countries may not translate equally well to other contexts. An evidence gap map for RTI is the first step towards understanding what evidence is available, from where, and the key gaps in knowledge.

Objectives

The objective of this evidence gap map (EGM) is to identify existing evidence from all effectiveness studies and systematic reviews related to road safety interventions. In addition, the EGM identifies gaps in evidence where new primary studies and systematic reviews could add value. This will help direct future research and discussions based on systematic evidence towards the approaches and interventions which are most effective in the road safety sector. This could enable the generation of evidence for informing policy at global, regional or national levels.

Search Methods

The EGM includes systematic reviews and impact evaluations assessing the effect of interventions for RTI reported in academic databases, organization websites, and grey literature sources. The studies were searched up to December 2019.

Selection Criteria

The interventions were divided into five broad categories: (a) human factors (e.g., enforcement or road user education), (b) road design, infrastructure and traffic control, (c) legal and institutional framework, (d) post-crash pre-hospital care, and (e) vehicle factors (except car design for occupant protection) and protective devices. Included studies reported two primary outcomes: fatal crashes and non-fatal injury crashes; and four intermediate outcomes: change in use of seat belts, change in use of helmets, change in speed, and change in alcohol/drug use. Studies were excluded if they did not report injury or fatality as one of the outcomes.

Data Collection and Analysis

The EGM is presented in the form of a matrix with two primary dimensions: interventions (rows) and outcomes (columns). Additional dimensions are country income groups, region, quality level for systematic reviews, type of study design used (e.g., case-control), type of road user studied (e.g., pedestrian, cyclists), age groups, and road type. The EGM is available online where the matrix of interventions and outcomes can be filtered by one or more dimensions. The webpage includes a bibliography of the selected studies and titles and abstracts available for preview. Quality appraisal for systematic reviews was conducted using a critical appraisal tool for systematic reviews, AMSTAR 2.

Main Results

The EGM identified 1859 studies of which 322 were systematic reviews, 7 were protocol studies and 1530 were impact evaluations. Some studies included more than one intervention, outcome, study method, or study region. The studies were distributed among intervention categories as: human factors (n = 771), road design, infrastructure and traffic control (n = 661), legal and institutional framework (n = 424), post-crash pre-hospital care (n = 118) and vehicle factors and protective devices (n = 111). Fatal crashes as outcomes were reported in 1414 records and non-fatal injury crashes in 1252 records. Among the four intermediate outcomes, speed was most commonly reported (n = 298) followed by alcohol (n = 206), use of seatbelts (n = 167), and use of helmets (n = 66). Ninety-six percent of the studies were reported from high-income countries (HIC), 4.5% from upper-middle-income countries, and only 1.4% from lower-middle and low-income countries. There were 25 systematic reviews of high quality, 4 of moderate quality, and 293 of low quality.

Authors' Conclusions

The EGM shows that the distribution of available road safety evidence is skewed across the world. A vast majority of the literature is from HICs. In contrast, only a small fraction of the literature reports on the many LMICs that are fast expanding their road infrastructure, experiencing rapid changes in traffic patterns, and witnessing growth in road injuries. This bias in literature explains why many interventions that are of high importance in the context of LMICs remain poorly studied. Besides, many interventions that have been tested only in HICs may not work equally effectively in LMICs. Another important finding was that a large majority of systematic reviews are of low quality. The scarcity of evidence on many important interventions and lack of good quality evidence-synthesis have significant implications for future road safety research and practice in LMICs. The EGM presented here will help identify priority areas for researchers, while directing practitioners and policy makers towards proven interventions.

Syncope While Driving and the Risk of a Subsequent Motor Vehicle Crash

STUDY OBJECTIVE

Syncope that occurs while driving can result in a motor vehicle crash. Whether individuals with a prior syncope-related crash exhibit an exceptional risk of subsequent crash remains uncertain.

METHODS

We performed a population-based retrospective observational study of patients diagnosed with 'syncope and collapse' at any of 6 emergency departments in British Columbia, Canada (2010 to 2015). Data were obtained from chart abstraction, administrative health records, insurance claims and police crash reports. We compared crash-free survival among individuals with crash-associated syncope (a crash and an emergency visit for syncope on the same date) to that among controls with syncope alone (no crash on date of emergency visit for syncope).

RESULTS

In the year following their index emergency visit, 13 of 63 drivers with crash-associated syncope and 852 of 9,160 controls with syncope alone experienced a subsequent crash as a driver (crash risk 21% versus 9%). After accounting for censoring and potential confounders, crash-associated syncope was not associated with a significant increase in the risk of subsequent crash (adjusted hazard ratio [aHR] 1.38, 95% confidence interval [CI] 0.78 to 2.47). Individuals with crash-associated syncope were 31-fold more likely to have physician driving advice documented during their index visit (prevalence ratio 31.0, 95% CI, 21.3 to 45.1). In the subgroup without documented driving advice, crash-associated syncope was associated with a significant increase in subsequent crash risk (aHR 1.88, 95% CI 1.06 to 3.36).

CONCLUSIONS

Crash risk after crash-associated syncope appears similar to crash risk after syncope alone.

Informing traffic enforcement leniency and discretion: Crash culpability and the effectiveness of written warnings versus citations

OBJECTIVES

Deterrence of risky driving behavior is important for the prevention of crashes and injuries. Traffic law enforcement is a key strategy used to decrease risky driving, but there is little evidence on the deterrent effect of issuing warnings versus citations to drivers regarding the prevention of future crashes. The purpose of this study was to 1) investigate the difference between citations and written warnings in their association with future crash culpability and 2) investigate whether drivers who were issued written warnings or citations have different associations with future crash culpability likelihood than those without prior citations or written warnings.

METHODS

Data for this study included Iowa Department of Transportation crash data for 2016 to 2019 linked to data from the Iowa Court Case Management System. A quasi-induced exposure method was used based on driver pairs involved in the same collision in which one driver was deemed culpable and one was non-culpable. Conditional logistic regression models were constructed to examine predictors of crash culpability. The main independent variable was traffic citation and warnings history categorized into moving warning, non-moving warning, moving citation, non-moving citation, or no citation or warning in the 30 days prior to the crash.

RESULTS

The study sample included a total of 152,986 drivers. Among drivers with moving violations, previously cited drivers were more likely to be crash culpable than previously warned drivers (OR = 1.64, 95% CI = 1.29-2.08). Drivers with prior non-moving citations were less likely to be the culpable party in a crash than a driver who had no recent warnings or citations (OR = 0.72, 95% CI = 0.58-0.89). Drivers with prior warnings (moving or non-moving) did not appreciably differ in crash culpability relative to drivers who had not received any citations or warnings in the previous 30 days.

CONCLUSIONS

Drivers with prior moving citations were more likely to be culpable in a future crash than drivers with prior moving warnings, which may relate to overall driving riskiness as opposed to effectiveness of citations in deterring risky driving behaviors. Results from this study also suggest that officer discretion was being appropriately applied by citing the riskiest drivers, while giving lower risk drivers warnings. Results from this study may be useful to support strengthening of state driver improvement programming.

Syncope and subsequent traffic crash: A responsibility analysis

BACKGROUND

Physicians are often asked to counsel patients about driving safety after syncope, yet little empirical data guides such advice.

METHODS

We identified a population-based retrospective cohort of 9,507 individuals with a driver license who were discharged from any of six urban emergency departments (EDs) with a diagnosis of 'syncope and collapse'. We examined all police-reported crashes that involved a cohort member as a driver and occurred between 1 January 2010 and 31 December 2016. We categorized crash-involved drivers as 'responsible' or 'non-responsible' for their crash using detailed police-reported crash data and a validated responsibility scoring tool. We then used logistic regression to test the hypothesis that recent syncope was associated with driver responsibility for crash.

RESULTS

Over the 7-year study interval, cohort members were involved in 475 police-reported crashes: 210 drivers were deemed responsible and 133 drivers were deemed non-responsible for their crash; the 132 drivers deemed to have indeterminate responsibility were excluded from further analysis. An ED visit for syncope occurred in the three months leading up to crash in 11 crash-responsible drivers and in 5 crash-non-responsible drivers, suggesting that recent syncope was not associated with driver responsibility for crash (adjusted odds ratio, 1.31; 95%CI, 0.40-4.74; p = 0.67). However, all drivers with cardiac syncope were deemed responsible, precluding calculation of an odds ratio for this important subgroup.

CONCLUSIONS

Recent syncope was not significantly associated with driver responsibility for traffic crash. Clinicians and policymakers should consider these results when making fitness-to-drive recommendations after syncope.

Analysis and Prediction of Vehicle Kilometers Traveled: A Case Study in Spain

Knowledge of the kilometers traveled by vehicles is essential in transport and road safety studies as an indicator of exposure and mobility. Its application in the determination of user risk indices in a disaggregated manner is of great interest to the scientific community and the authorities in charge of ensuring road safety on highways. This study used a sample of the data recorded during passenger vehicle inspections at Vehicle Technical Inspection stations and housed in a data warehouse managed by the General Directorate for Traffic of Spain. This study has three notable characteristics: (1) a novel data source is explored, (2) the methodology developed applies to other types of vehicles, with the level of disaggregation the data allows, and (3) pattern extraction and the estimate of mobility contribute to the continuous and necessary improvement of road safety indicators and are aligned with goal 3 (Good Health and Well-Being: Target 3.6) of The United Nations Sustainable Development Goals of the 2030 Agenda. An Operational Data Warehouse was created from the sample received, which helped in obtaining inference values for the kilometers traveled by Spanish fleet vehicles with a level of disaggregation that, to the knowledge of the authors, was unreachable with advanced statistical models. Three machine learning methods, CART, random forest, and gradient boosting, were optimized and compared based on the performance metrics of the models. The three methods identified the age, engine size, and tare weight of passenger vehicles as the factors with greatest influence on their travel patterns.

Driver Liability Assessment in Vehicle Collisions in Spain

An accurate estimation of exposure is essential for road collision rate estimation, which is key when evaluating the impact of road safety measures. The quasi-induced exposure method was developed to estimate relative exposure for different driver groups based on its main hypothesis: the not-at-fault drivers involved in two-vehicle collisions are taken as a random sample of driver populations. Liability assignment is thus crucial in this method to identify not-at-fault drivers, but often no liability labels are given in collision records, so unsupervised analysis tools are required. To date, most researchers consider only driver and speed offences in liability assignment, but an open question is if more information could be added. To this end, in this paper, the visual clustering technique of self-organizing maps (SOM) has been applied to better understand the multivariate structure in the data, to find out the most important variables for driver liability, analyzing their influence, and to identify relevant liability patterns. The results show that alcohol/drug use could be influential on liability and further analysis is required for disability and sudden illness. More information has been used, given that a larger proportion of the data was considered. SOM thus appears as a promising tool for liability assessment.

Prescription medication use as a risk factor for motor vehicle collisions: a responsibility study

INTRODUCTION

Previous studies on the effect of prescription medications on MVCs are sparse, not readily applicable to real-world driving and/or subject to strong selection bias. This study examines whether the presence of prescription medication in drivers' blood is associated with being responsible for MVC.

METHODS

This modified case-control study with responsibility analysis compares MVC responsibility rates among drivers with detectable levels of six classes of prescription medications (anticonvulsants, antidepressants, antihistamines, antipsychotics, benzodiazepines, opioids) versus those without. Data were collected between January 2010 and July 2016 from emergency departments in British Columbia, Canada. Collision responsibility was assessed using a validated and automated scoring of police collision reports. Multivariable logistic regression was used to determine OR of responsibility (analysed in 2018-2019).

RESULTS

Unadjusted regression models show a significant association between anticonvulsants (OR 1.92; 95% CI 1.20 to 3.09; p=0.007), antipsychotics (OR 5.00; 95% CI 1.16 to 21.63; p=0.03) and benzodiazepines (OR 2.99; 95% CI 1.56 to 5.75; p=0.001) with collision responsibility. Fully adjusted models show a significant association between benzodiazepines with collision responsibility (aOR 2.29; 95% CI 1.16 to 4.53; p=0.02) after controlling for driver characteristics, blood alcohol and Δ-9-tetrahydrocannabinol concentrations, and the presence of other prescription medications. Antidepressants, antihistamines and opioids exhibited no significant associations.

CONCLUSION

There is a moderate increase in the risk of a responsible collision among drivers with detectable levels of benzodiazepines in blood. Physicians and pharmacists should consider collision risk when prescribing or dispensing benzodiazepines. Public education about benzodiazepine use and driving and change to traffic policy and enforcement measures are warranted.

Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study

AIM

We conducted a responsibility analysis to determine whether drivers injured in motor vehicle collisions who test positive for Δ-9-tetrahydrocannabinol (THC) or other drugs are more likely to have contributed to the crash than those who test negative.

DESIGN

Prospective case-control study.

SETTING

Trauma centres in British Columbia, Canada.

PARTICIPANTS

Injured drivers who required blood tests for clinical purposes following a motor vehicle collision.

MEASUREMENTS

Excess whole blood remaining after clinical use was obtained and broad-spectrum toxicology testing performed. The analysis quantified alcohol and THC and gave semiquantitative levels of other impairing drugs and medications. Police crash reports were analysed to determine which drivers contributed to the crash (responsible) and which were 'innocently involved' (non-responsible). We used unconditional logistic regression to determine the likelihood (odds ratio: OR) of crash responsibility in drivers with 0 < THC < 2 ng/ml, 2 ng/ml ≤ THC < 5 ng/ml and THC ≥ 5 ng/ml (all versus THC = 0 ng/ml). Risk estimates were adjusted for age, sex and presence of other impairing substances.

FINDINGS

We obtained toxicology results on 3005 injured drivers and police reports on 2318. Alcohol was detected in 14.4% of drivers, THC in 8.3%, other drugs in 8.9% and sedating medications in 19.8%. There was no increased risk of crash responsibility in drivers with THC < 2 ng/ml or 2 ≤ THC < 5 ng/ml. In drivers with THC ≥ 5 ng/ml, the adjusted OR was 1.74 [95% confidence interval (CI) = 0.59-6.36; P = 0.35]. There was significantly increased risk of crash responsibility in drivers with blood alcohol concentration (BAC) ≥ 0.08% (OR = 6.00;95% CI = 3.87-9.75; P < 0.01), other recreational drugs detected (OR = 1.82;95% CI = 1.21-2.80; P < 0.01) or sedating medications detected (OR = 1.45; 95%CI = 1.11-1.91; P < 0.01).

CONCLUSIONS

In this sample of non-fatally injured motor vehicle drivers in British Columbia, Canada, there was no evidence of increased crash risk in drivers with Δ-9-tetrahydrocannabinol < 5 ng/ml and a statistically non-significant increased risk of crash responsibility (odds ratio = 1.74) in drivers with Δ-9-tetrahydrocannabinol ≥ 5 ng/ml.

Changing patterns of motor vehicle collision risk during winter storms: A new look at a pervasive problem

Past research has shown that winter precipitation is an important environmental factor that increases the frequency of motor vehicle collisions that cause personal injury and property damage. Questions remain about the magnitude of winter storm effects on collision occurrence, changes in risk over time, and the role of driver behaviour in conjunction with other factors (e.g., winter maintenance by road authorities) as it affects exposure and sensitivity to hazardous conditions. In response, a matched-pair, retrospective cohort method was used to estimate injury and non-injury collision risks for a mid-sized urban community based on a new definition of winter storm events that, relative to previous studies, captures a greater portion of time during which drivers respond to hazardous weather and road surface conditions. Winter storm definition criteria were applied to weather radar imagery and traditional surface station observations in a unique manner to classify and characterize a set of 196 variable-length storm events in terms of precipitation type and amount, visibility, temperature profile, presence of government-issued warnings, location, and temporal factors. Injury and non-injury collisions increased by 66 and 137 percent, respectively, during winter storms relative to dry weather conditions. Although these increases were higher than findings from similar studies of winter precipitation events conducted over the same timeframe (i.e., 2002-2016), they were found to have declined by a statistically significant amount over the course of the study period and disproportionately to collisions in general. Understanding why this is occurring, and then attributing improvements to specific winter road safety interventions and behavioural adjustments, is a key focus for future research and for informing future risk-mitigating investments.

Methods for investigating crash risk: Comparing case-control with responsibility analysis

OBJECTIVE

There are 2 primary methods for establishing relative risk: case-control studies, in which crash and matched control data are collected separately, and responsibility analysis, which exploits a single existing crash database by using nonresponsible drivers as an "induced exposure" control group (which is less expensive and therefore more feasible for examining the large number of substances that can impact driving behavior). Though both approaches are scientifically sound and methodologically valid, each approach has its own inherent obstacles to overcome. In this article, we examine in detail how different criteria for the development of control cases influence the accuracy of crash risk estimates for drivers with positive blood alcohol concentrations (BACs).

METHODS

We applied responsibility analysis to crash-involved drivers in a recent crash case-control study, thereby providing 2 sets of control cases: Those from responsibility analysis and those from the case control study.

RESULTS

Case-control and responsibility analysis crash risk curves did not differ significantly, indicating that both systems generate valid estimates of the relative crash risk of drivers on the road.

CONCLUSIONS

The results suggest that when researchers are faced with finance or time constraints that make case-control studies infeasible, responsibility analysis should be considered a viable alternate methodological approach.

Challenges and common weaknesses in case-control studies on drug use and road traffic injury based on drug testing of biological samples

PURPOSE

To determine and discuss common weaknesses and errors in case-control studies on the association between drug use and road traffic crash injury among drivers and recommend improvements for future studies.

METHODS

A search for case-control studies published between 2000 and 2016 was performed using PubMed and other databases in addition to manual search. The used methodologies were compared with requirements and recommendations for case-control studies as well as current knowledge on the interpretation of drug concentrations in biological samples.

RESULTS

Seventeen studies were identified. The major difficulties in the studies were related to likely selection bias, information bias, and confounding. In some studies, the definition of drug exposure was different for controls than for cases, generating potentially serious errors in the odds ratio estimations. Other weaknesses include lacking explanation of the assessment of drug exposure, missing covariates, lacking description of statistical methods, and lack of discussion of bias and confounding.

CONCLUSIONS

Many of the observed challenges and weaknesses can be overcome or reduced. Recommendations for future studies are presented.

Risk factors for motorcycle loss-of-control crashes

OBJECTIVE

The present article identifies and assesses the effect of critical factors on the risk of motorcycle loss-of-control (LOC) crashes.

METHOD

Data come from a French project on road crashes, which include all fatal road crashes and a random sample of 1/20th of nonfatal crashes in France in 2011, based on police reports. A case-control study was carried out on a sample of 903 crashes for 444 LOC motorcycle riders (case) and 470 non-LOC and nonresponsible motorcycle riders (control). The sample was weighted due to the randomization of nonfatal crashes. Missing values were imputed using multiple imputation.

RESULTS

Road alignment and surface conditions, human factors, and motorcycle type played important roles in motorcycle LOC crashes. Riding in a curve was associated with a 3-fold greater risk of losing control of motorcycle than riding in a straight line. Poor road adhesion significantly increased the risk of losing control; the risk increased more than 20-fold when deteriorated road adhesion was encountered unexpectedly, due to loose gravel, ice, oil, bumps, road marking, metal plates, etc. For motorcyclists, riding with a positive blood alcohol concentration (over or equal to the legal limit of 0.5 g/L) was very dangerous, often resulting in losing control. The risk of LOC crash varied for different types of motorcycle: Riders of roadsters and sports bikes were more likely to have an LOC crash greater than that of riders of basic or touring motorcycles. In addition, LOC risk increased with speed; a model using the square of the traveling speed showed better fit than one using speed itself.

CONCLUSION

The LOC crash factors related to riders, vehicles, and road infrastructure identified here were expected but were rarely identified and taken simultaneously into account in previous studies. They could be targeted by countermeasures to improve motorcyclist safety.

Cannabis, alcohol and fatal road accidents

Introduction

This research aims to estimate the relative risks of responsibility for a fatal accident linked to driving under the influence of cannabis or alcohol, the prevalence of these influences among drivers and the corresponding attributable risk ratios. A secondary goal is to estimate the same items for three other groups of illicit drugs (amphetamines, cocaine and opiates), and to compare the results to a similar study carried out in France between 2001 and 2003.

Methodology

Police procedures for fatal accidents in Metropolitan France during 2011 were analyzed and 300 characteristics encoded to provide a database of 4,059 drivers. Information on alcohol and four groups of illicit drugs derived from tests for positivity and potential confirmation through blood analysis. The study compares drivers responsible for causing the accident, that is to say having directly contributed to its occurrence, to drivers involved in an accident for which they were not responsible, and who can be assimilated to drivers in general.

Results

The proportion of persons driving under the influence of alcohol is estimated at 2.1% (95% CI: 1.4–2.8) and under the influence of cannabis at 3.4% (2.9%-3.9%). Drivers under the influence of alcohol are 17.8 times (12.1–26.1) more likely to be responsible for a fatal accident, and the proportion of fatal accidents which would be prevented if no drivers ever exceeded the legal limit for alcohol is estimated at 27.7% (26.0%-29.4%). Drivers under the influence of cannabis multiply their risk of being responsible for causing a fatal accident by 1.65 (1.16–2.34), and the proportion of fatal accidents which would be prevented if no drivers ever drove under the influence of cannabis is estimated at 4.2% (3.7%-4.8%). An increased risk linked to opiate use has also been found to be significant, but with low prevalence, requiring caution in interpreting this finding. Other groups of narcotics have even lower prevalence, and the associated extra risks cannot be assessed.

Conclusion

Almost a decade separates the present study from a similar one previously conducted in France, and there have been numerous developments in the intervening years. Even so, the prevalence of drivers responsible for causing fatal accidents under the influence of alcohol or narcotics has stayed remarkably stable, as have the proportion of fatal accidents which could in theory be prevented if no drivers ever exceeded the legal limits. The overall number of deaths from traffic accidents has dropped sharply during this period, and the number of victims attributable to alcohol and/or cannabis declined proportionally. Alcohol remains the main problem in France. It is just as important to note that one in two drivers considered to be under the influence of cannabis was also under the influence of alcohol. With risks cumulating between the two, it is particularly important to point out the danger of consuming them together.

The epidemiologic principles underlying traffic safety study designs

This article describes the epidemiological principles underlying four observational study designs commonly used to assess traffic safety: the case-control, case-crossover, culpability and quasi-induced exposure designs. We focus in particular on the specific challenges for preventing bias using each design. Whereas recruiting controls representative of the source population poses a special challenge in case-control traffic safety studies, case-crossover designs are prone to recall bias, and culpability and quasi-induced exposure studies can be undermined by difficulties assigning crash responsibility. Using causal diagrams and worked examples, we provide a simple way to teach traffic safety designs to epidemiologists and to encourage proper application of epidemiological principles among researchers designing traffic safety studies.

Gender and age differences in components of traffic-related pedestrian death rates: exposure, risk of crash and fatality rate

Background

This ecological study aimed i) to quantify the association of age and gender with the three components of pedestrians’ death rates after a pedestrian-vehicle crash: exposure, risk of crash and fatality, and ii) to determine the contribution of each component to differences in death rates according to age and gender in Spain.

Methods

We analyzed data for 220 665 pedestrians involved in road crashes recorded in the Spanish registry of road crashes with victims from 1993 to 2011, and a subset of 39 743 pedestrians involved in clean collisions (in which the pedestrian did not commit an infraction). Using decomposition and quasi-induced exposure methods, we obtained the proportion of increase in death rates for each age and gender group associated with exposure, risk of collision and fatality.

Results

Death rates increased with age. The main contributor to this increase was fatality, although exposure also increased with age. In contrast, the risk of collision decreased with age. Males had higher death rates than females, especially in the 24–54 year old group. Higher fatality rates in males were the main determinant of this difference, which was also related with a higher risk of collision in males. However, exposure rates were higher in females.

Conclusions

The magnitude and direction of the associations between age and gender and each of the three components of pedestrians’ death rates differed depending on the specific component explored. These differences need to be taken into account in order to prioritize preventive strategies intended to decrease mortality among pedestrians.

Electronic supplementary material

The online version of this article (doi:10.1186/s40621-016-0079-2) contains supplementary material, which is available to authorized users.

Modelling crash propensity of carshare members

Carshare systems are considered a promising solution for sustainable development of cities. To promote carsharing it is imperative to make them cost effective, which includes reduction in costs associated to crashes and insurance. To achieve this goal, it is important to characterize carshare users involved in crashes and understand factors that can explain at-fault and not-at fault drivers. This study utilizes data from GoGet carshare users in Sydney, Australia. Based on this study it was found that carshare users who utilize cars less frequently, own one or more cars, have less number of accidents in the past ten years, have chosen a higher insurance excess and have had a license for a longer period of time are less likely to be involved in a crash. However, if a crash occurs, carshare users not needing a car on the weekend, driving less than 1000km in the last year, rarely using a car and having an Australian license increases the likelihood to be at-fault. Since the dataset contained information about all members as well as not-at-fault drivers, it provided a unique opportunity to explore some aspects of quasi-induced exposure. The results indicate systematic differences in the distribution between the not-at-fault drivers and the carshare members based on the kilometres driven last year, main mode of travel, car ownership status and how often the car is needed. Finally, based on this study it is recommended that creating an incentive structure based on training and experience (based on kilometres driven), possibly tagged to the insurance excess could improve safety, and reduce costs associated to crashes for carshare systems.

Why has the pedestrian death rate decreased in Spain between 1993 and 2011? An application of the decomposition method

A decomposition procedure was used to estimate the percentage contributions of exposure, risk of collision and fatality to explain the decreases in pedestrian collision death rates observed in Spain from 1993 to 2011. Information was obtained from the Spanish National Institute of Statistics and the Spanish Register of Road Crashes with Victims. A quasi-induced method was used to obtain estimates of annual pedestrian exposure. Poisson regression was used to obtain age-adjusted and sex-adjusted estimates of the mean annual percentage decrease in pedestrian death rates attributable to exposure, collision and fatality; these values were +2.28%, -45.86% and -51.86%, respectively. The results suggest that the decrease in fatality rates and, to a lesser extent, collision rates were the most important determinants of the reduction in pedestrian collision death rates, whereas the contribution of exposure was irrelevant.

A comprehensive review on the quasi-induced exposure technique

OBJECTIVE

The goal is to comprehensively examine the state-of-the-art applications and methodological development of quasi-induced exposure and consequently pinpoint the future research directions in terms of implementation guidelines, limitations, and validity tests.

METHODS

The paper conducts a comprehensive review on approximately 45 published papers relevant to quasi-induced exposure regarding four key topics of interest: applications, responsibility assignment, validation of assumptions, and methodological development.

RESULTS

Specific findings include that: (1) there is no systematic data screening procedure in place and how the eliminated crash data will impact the responsibility assignment is generally unknown; (2) there is a lack of necessary efforts to assess the validity of assumptions prior to its application and the validation efforts are mostly restricted to the aggregated levels due to the limited availability of exposure truth; and (3) there is a deficiency of quantitative analyses to evaluate the magnitude and directions of bias as a result of injury risks and crash avoidance ability.

CONCLUSIONS

The paper points out the future research directions and insights in terms of the validity tests and implementation guidelines.

Association of cyclists' age and sex with risk of involvement in a crash before and after adjustment for cycling exposure

This study aimed to estimate the association of cyclists' age and sex with the risk of being involved in a crash with and without adjustment for their amount of exposure. We used the distribution of the entire population and cyclists (total and non-responsible) involved in road crashes in Spain between 1993 and 2009 held by the Spanish National Institute of Statistics and the Spanish General Traffic Directorate to calculate rates of exposure and involvement in a crash. Males aged 45-49 years were used as the reference category to obtain exposure rate ratios (ERR) and unadjusted crash rate ratios (URR). We then used these values in decomposition analysis to calculate crash rate ratios adjusted for exposure (ARR). The pattern of ARR was substantially different from URR. In both sexes the highest values were observed in the youngest age groups, and the values decreased as age increased except for a slight increase in the oldest age groups. In males, a slight increase in the lowest and highest age categories was observed for crashes resulting in severe injury or death, and a decrease was observed for the youngest cyclists who were wearing a helmet. The large differences between age and sex groups in the risk of involvement in a cycling crash are strongly dependent on differences in their exposure rates. Taking exposure rates into account, cyclists younger than 30 years and older than 65 years of age had the highest risk of being involved in a crash.

The use of self-report exposure measures among novice motorcyclists: appropriateness and best practice recommendations

OBJECTIVES

While self-report methods to collect exposure information have large practical advantages in many research contexts, little research has specifically investigated the reliability and validity of motorcyclists' self-reported exposure. The present study aimed to examine the reliability and validity of different self-report exposure measures and to provide recommendations on best practice self-report riding exposure questions.

METHODS

The reliability and validity of different self-report exposure measures were examined amongst novice motorcyclists through t-tests, Bland Altman plots, coefficients of variation, and correlations.

RESULTS

The most valid and reliable data was provided when riding exposure was asked for the current average week rather than earlier and longer periods, and in units of time rather than distance or number of trips. The greater reliability of riding exposure found amongst commuting and rural riders compared to recreational and metropolitan riders respectively and at the second interview compared to the first suggests that factors such as riding purposes, geographical locations, and riding experience can contribute to measurement error.

CONCLUSIONS

If self-reported odometer readings are used, questions on whether the respondents share their own bike or ride more than one bike, and a built-in process to ensure respondents report the exact odometer reading on their bike are recommended. It is recommended that self-report riding exposure questions ask about the hours of riding for the current average week, and data on riding purposes, locations, and experience are also collected.

Risk of road accident associated with the use of drugs: a systematic review and meta-analysis of evidence from epidemiological studies

This paper is a corrigendum to a previously published paper where errors were detected. The errors have been corrected in this paper. The paper is otherwise identical to the previously published paper. A systematic review and meta-analysis of studies that have assessed the risk of accident associated with the use of drugs when driving is presented. The meta-analysis included 66 studies containing a total of 264 estimates of the effects on accident risk of using illicit or prescribed drugs when driving. Summary estimates of the odds ratio of accident involvement are presented for amphetamines, analgesics, anti-asthmatics, anti-depressives, anti-histamines, benzodiazepines, cannabis, cocaine, opiates, penicillin and zopiclone (a sleeping pill). For most of the drugs, small or moderate increases in accident risk associated with the use of the drugs were found. Information about whether the drugs were actually used while driving and about the doses used was often imprecise. Most studies that have evaluated the presence of a dose-response relationship between the dose of drugs taken and the effects on accident risk confirm the existence of a dose-response relationship. Use of drugs while driving tends to have a larger effect on the risk of fatal and serious injury accidents than on the risk of less serious accidents (usually property-damage-only accidents). The quality of the studies that have assessed risk varied greatly. There was a tendency for the estimated effects of drug use on accident risk to be smaller in well-controlled studies than in poorly controlled studies. Evidence of publication bias was found for some drugs. The associations found cannot be interpreted as causal relationships, principally because most studies do not control very well for potentially confounding factors.

Using speeding detections and numbers of fatalities to estimate relative risk of a fatality for motorcyclists and car drivers

Precise estimation of the relative risk of motorcyclists being involved in a fatal accident compared to car drivers is difficult. Simple estimates based on the proportions of licenced drivers or riders that are killed in a fatal accident are biased as they do not take into account the exposure to risk. However, exposure is difficult to quantify. Here we adapt the ideas behind the well known induced exposure methods and use available summary data on speeding detections and fatalities for motorcycle riders and car drivers to estimate the relative risk of a fatality for motorcyclists compared to car drivers under mild assumptions. The method is applied to data on motorcycle riders and car drivers in Victoria, Australia in 2010 and a small simulation study is conducted.

Risk factors for causing road crashes involving cyclists: An application of a quasi-induced exposure method

A quasi-induced exposure approach was applied to the Spanish Register of Traffic Crashes to identify driver- and vehicle-related factors associated with the risk of causing a road crash involving a cyclist in Spain from 1993 to 2009. We analyzed 19,007 collisions between a bicycle and another vehicle in which only one of the drivers committed an infraction, and 13,540 records that included the group of non-infractor cyclists in the above collisions plus cyclists involved in single-bicycle crashes. Adjusted odds ratios were calculated for being responsible for each type of crash for each factor considered. Age from 10 to 19 years, male sex, alcohol or drug consumption and non-helmet use were cyclist-related variables associated with a higher risk of crash, whereas cycling more than 1h increased only the risk of single crashes. Bicycles with brake defects and ridden by two occupants were also at higher risk of involvement in a crash, whereas light defects were associated only with collisions with another vehicle. For drivers of the other vehicle, age more than 60 years, alcohol, not using safety devices and nonprofessional drivers were at higher risk. The risk of colliding with a bicycle was higher for mopeds than for passenger cars.

Development and validation of a crash culpability scoring tool

OBJECTIVE

Several traffic safety research techniques require researchers to separate crash-involved drivers into culpable and nonculpable. Nonculpable drivers are assumed to be randomly involved in crashes by external factors and to approximate a noncollision control population. If this is true, factors that increase crash risk should be found more often in culpable than in nonculpable drivers. Though a culpability scoring tool has been developed for research purposes, that tool does not adequately address winter driving conditions (Robertson and Drummer 1994). Moreover, traditional culpability scoring requires assessors to read and score individual collision reports. The purpose of this study is to develop and validate an automated, rule-based Canadian culpability scoring tool that is capable of rapidly scoring police crash reports from large administrative datasets.

METHODS

We used an iterative approach to develop and validate our tool. First, the Robertson-Drummer culpability scoring tool was modified to include the extensive police report data collected in the British Columbia Traffic Accident System (TAS) and to account for winter driving conditions. This was done in consultation with traffic safety experts. The scoring tool was automated, employing a rule-based decision model that avoids interpretation of free-text reports. The scoring tool was applied to 73 collisions (134 drivers). Two experts also reviewed these collisions and determined the culpability of each driver. Discrepant cases were discussed to understand why the scoring tool differed from the expert assessment and the scoring tool was modified accordingly. The final tool was compared with expert assessment on another sample of 96 crashes. The tool was also applied to a sample of 2086 crash-involved drivers with known blood alcohol concentrations (BACs) and the adjusted odds of culpability were calculated for several BAC ranges.

RESULTS

The final scoring tool included 7 factors and had content validity for traffic safety experts. It had excellent agreement with expert scoring on the first set of collisions (kappa = 0.83, 95% confidence interval [CI]: 0.75-0.91) and on the second set (kappa = 0.84, 95% CI: 0.77-0.92). When applied to crash-involved drivers with known BAC levels, the scoring tool exhibited predictive validity: the odds of culpability increased with higher BACs, consistent with the known dose effect of BAC on crash risk.

CONCLUSIONS

We have developed an automated culpability scoring tool contextualized to Canadian driving conditions. This tool will allow road safety researchers to assess collision responsibility in large administrative data sets derived from police reports.

Analysis of precipitation-related motor vehicle collision and injury risk using insurance and police record information for Winnipeg, Canada

INTRODUCTION

Police records are the most common source of data used to estimate motor-vehicle collision risks, understand causal or contributing factors, and evaluate the efficacy of interventions. The literature notes concerns about this information citing discrepancies between police reports and other sources of injury occurrence and severity data. The primary objective of the analysis was to assess the adequacy of police reports for an examination of weather-related injury collision risk.

METHOD

Analyses of relative risk were carried out using both police records and comprehensive insurance claim data for Winnipeg, Canada over the period 1999-2001.

RESULTS AND CONCLUSIONS

Both data sets yielded very similar results-precipitation substantially increases the risk of injury collision (police records: RR 1.76, CI 1.55-2.00; insurance: RR 1.80, CI 1.62-1.99) and risk of injury (police records, RR 1.74, CI 1.55-1.96; insurance, RR 1.69, CI 1.55-1.85) relative to corresponding dry weather control periods. Both rainfall and snowfall were associated with large increases in collisions and injuries.

IMPACT ON INDUSTRY

While relative risks are almost identical, over 64% more injury collisions and 74% more injuries were identified using the insurance data, which is an important difference for evaluating absolute risk and exposure.

Last Call: decreasing drunk driving among 21-34-year-old bar patrons

Any effort to decrease the toll of drunk driving must include efforts directed at people who drink in bars, particularly young adults who use motor vehicles after drinking. We designed a multifaceted social marketing campaign, Last Call, to increase the use of designated drivers and safe rides homes among 21-34-year olds. There were three components to the intervention: (1) use of taxi stands to promote taxi use; (2) point-of-sale information to patrons at partner bars and (3) a mass media campaign to support the designated driver/safe ride home message. Among the heaviest drinkers, the programme significantly increased the use of designated drivers and increased the use of taxis by 63%.

Comparison of two methods to assess the effect of age and sex on the risk of car crashes

BACKGROUND

This study was designed to compare two methods (direct measurement of exposure and quasi-induced exposure) for assessing the effect of age and sex on the risk of being involved in a car crash in Spain.

METHODS

Spanish crash rates (per 10,000,000 driver-km) for age and sex groups of drivers aged 18-64 years old were obtained for 2004-2007, using information from the Spanish General Traffic Office (census of reported car crashes) and the Spanish Household Survey on Alcohol and Drugs (estimate of the mean km driven for each car driver). The rate ratios estimated by direct exposure estimates were compared to those obtained with the quasi-induced exposure method, which compares the age and sex of responsible and non-responsible drivers involved in the same clean collision (in which only one of the drivers committed a driving infraction).

RESULTS

Both methods detected an increased risk of involvement in a crash for the youngest (18-20 years) and the oldest drivers (60-64 years), compared to middle-aged drivers (45-49 years). However, the rate ratios obtained with the quasi-induced method for the youngest group (2.0 for men, 1.6 for women) were much lower than those obtained with crash rates (13.4 for men, 5.7 for women). Both methods detected a similar increase in the risk of involvement of male drivers compared to women in the youngest age group. This excess risk for men was maintained with increasing age up to 45-49 years when the quasi-induced method was used. However, direct comparisons of crash rates revealed an increased risk of involvement in women compared to men of the same age from 25-29 years onward.

CONCLUSIONS

Both direct measurement of driving exposure and the quasi-induced exposure method detected some well-known patterns of risk associated with driver's age and sex. However, factors that could explain important differences between the two methods deserve attention, especially those related with the excess risk for the youngest drivers as well as sex-related risk.

Diseases, consumption of medicines and responsibility for a road crash: a case-control study

The role of medical conditions in crashes is a topic of public debate. Some studies suggest that there has been a reduction in road traffic crashes subsequent to the medical restrictions introduced on drivers with medical deficiencies. As in today's society the car is an important factor for independence and socialization, it seems important to consider whether diseases or consumption of drugs increase the risk of causing a road crash in comparison to well-known major crash risk factors. A case-control study was conducted (733 injured drivers). The cases were subjects who were partly or totally responsible for their crash. The 304 controls were the non-responsible drivers. Diseases and medicine consumption were analyzed using logistic regression models. Cases were characterized by a higher percentage of young men. They were more frequently affected by fatigue, as were subjects who had consumed alcohol. A higher risk in subjects suffering from hypertension is observed (adjusted odds ratio [adjOR]=3.82; 95%CI=[1.42-10.24]). An association between antidepressant consumption and responsibility appeared (adjOR=3.61; 95%CI=[1.30-10.03]).

CONCLUSION

Medical factors associated with responsibility were arterial hypertension and antidepressant consumption. Other medical conditions do not seem to play a preponderant role comparing to individual behaviours.