Nadia Mullen

The combined effects of alcohol and cannabis on driving: Impact on crash risk

BACKGROUND/OBJECTIVES Driving under the influence of alcohol or cannabis alone is associated with increased crash risk. This study explores the combined influence of low levels of alcohol (BAC≤0.08) and cannabis on crash risk. MATERIALS AND METHODS Drivers aged 20 years or older who had been tested for both drugs and alcohol after involvement in a fatal crash in the United States (1991-2008) were examined using a case-control design. Cases were drivers with at least one potentially unsafe driving action (UDA) recorded in relation to the crash (e.g., weaving); controls had none recorded. We examined the prevalence of driving under the influence of alcohol, cannabis, and both agents, for drivers involved in a fatal crash. Adjusted odds ratios of committing an UDA for alcohol alone, THC alone, and their combined effect were computed via logistic regression and adjusted for a number of potential confounders. RESULTS Over the past two decades, the prevalence of THC and alcohol in car drivers involved in a fatal crash has increased approximately five-fold from below 2% in 1991 to above 10% in 2008. Each 0.01 BAC unit increased the odds of an UDA by approximately 9-11%. Drivers who were positive for THC alone had 16% increased odds of an UDA. When alcohol and THC were combined the odds of an UDA increased by approximately 8-10% for each 0.01 BAC unit increase over alcohol or THC alone. CONCLUSION Drivers positive for both agents had greater odds of making an error than drivers positive for either alcohol or cannabis only. Further research is needed to better examine the interaction between cannabis concentration levels, alcohol, and driving. This research would support enforcement agencies and public health educators by highlighting the combined effect of cannabis at low BAC levels.

Physiological responses to simulated and on-road driving

Driving simulators have become an increasingly popular tool to study and assess drivers. Physiological measurements not only provide an important index of an individuals presence in the virtual environment, but they also permit us to compare simulated and on-road experiences. However, at this point, few studies examining the ecological validity of simulated driving have included physiological variables. In a first study, we embedded three surprising events into a typical simulated road circuit. The first event consisted of a car pulling out suddenly from the shoulder of the road, while the remaining two events consisted of a green traffic light changing to amber as the driver approached the intersection. We noted statistically significant elevations in the mean heart rate (MHR) response to virtual events of about 4beats per minute (bpm) during the 15s immediately following the events. In a second study, we directly compared heart rate, oxygen consumption (VO(2)), and mean ventilation (MV(E)) responses to similar simulated and on-road drives. The change in physiological variables from baseline to driving was similar between simulated and on-road conditions, and a very strong correlation between simulated and on-road driving values for MV(E) (r=0.90) was observed. MHR and maximum heart rate (HR(max)) were nonetheless significantly higher during on-road drives. These studies suggest that the level of immersion of a fixed base simulator is great enough to elicit presence, and achieve both relative and absolute validity for certain physiological parameters. Nonetheless, the absolute responses between virtual and real world experiences remain different. For both research and evaluation purposes, it is critical that we better understand the impact of the drivers perceived level of risk or difficulty during simulation on their driving behaviour and physiological responses.

Aggressive driving behaviour in young drivers (aged 16 through 25) involved in fatal crashes

INTRODUCTION We wished to determine the extent to which number of passengers, driver age, and sex were associated with aggressive driving actions (ADAs) in young drivers involved in a fatal crash. METHODS We used U.S. fatal-crash data from Fatality Analysis Reporting System (FARS), 1991 -2008. Proxy measures of aggressive driving included ADA presence and speed differential (posted speed limit minus estimated travel speed). We examined the odds of an ADA and speed differential in young drivers (aged 16 to 25) by passenger status. RESULTS Compared to driving alone young drivers (aged 16) had increased odds of an ADA between 14% (OR: 1.14; 95% CI: 1.07; 1.22) and 95% (OR: 1.95; 95% CI: 1.40; 2.74) when accompanied by one and five passengers, respectively. Further, carrying a higher number of passengers was a stronger predictor of speeding in younger drivers. CONCLUSIONS This study supports the use of graduated licensing approaches. Specifically, developing interventions to reduce aggressive driving appear imperative. IMPACT ON INDUSTRY While the results of our study support the use of graduated licensing approaches there is room for improvement. Our study indicates that tackling impaired driving is not sufficient to drastically reduce aggressive driving among the youngest drivers. Further research on young drivers is required to understand the influence of peers and the role of gender on driving behavior. Strategies to reduce aggressive driving behaviors among the youngest drivers may not only prevent crashes during their early driving careers but may also translate into a reduced crash risk over their lifetime.

The Influence of Stimulants on Truck Driver Crash Responsibility in Fatal Crashes

INTRODUCTION Given the monotony and extended driving periods inherent in transport truck driving, drivers might rely on stimulants to sustain attention and combat fatigue. Research indicates that stimulant use improves some cognitive functions but impairs driving ability and is linked to crashes. The research on crash responsibility among stimulant-positive truck drivers is inconclusive due to small sample sizes and a lack of control over confounding variables. The present study investigated the influence of stimulants on unsafe driving actions (UDAs) in fatal crashes contained in the Fatality Analysis Reporting System (FARS) database. METHODS Logistic regression was used to calculate the odds ratio of an UDA (cases committed an UDA; controls did not) by stimulant status (present; absent) while accounting for the influence of confounding variables (age, previous driving record, and other drug use). RESULTS For all truck drivers, we found that 372 truck drivers tested stimulant-positive representing 0.57% of the entire truck driver sample and 3.7% of truck drivers who were actually tested for drug use. Stimulant-positive truck drivers had a greater proportion of driving record infractions and narcotic drug use compared to stimulant-negative truck drivers. The adjusted odds of committing an UDA were 78% greater for truck drivers who were stimulant-positive (OR: 1.78, 95% CI: 1.41-2.26) compared to truck drivers stimulant-negative. CONCLUSION The results suggest stimulants are associated with crash responsibility and warrant further study into their impact on truck drivers.

One- and Three-Screen Driving Simulator Approaches to Evaluate Driving Capacity: Evidence of Congruence and Participants’ Endorsement

OBJECTIVE We examined the validity of one-screen versus three-screen driving simulators and their acceptability to middle-aged and older drivers. METHOD Participants aged 40-55 or 65 and older (N = 32) completed simulated drives first with a single monitor and then with a three-monitor setup, followed by pen-and-paper measures and an interview. RESULTS Mean differences between one- and three-screen drives were not statistically significant for Starting/Stopping and Passing/Speed. Correlations between the two drives indicated moderate positive linear relationships with moderate agreement. More errors occurred on the one-screen simulator for Signal Violation/Right of Way/Inattention, Moving in a Roadway, Turning, and Total Scores. However, for Moving in a Roadway, Turning, and Total Scores, correlations between drives indicated strong positive linear relationships. We found no meaningful correlation between workload, computer comfort, simulator discomfort, and performance on either drive. Participants found driving simulators acceptable. CONCLUSION Findings support the use of one-screen simulators. Participants were favorable regarding driving simulators for assessment.

Looking Forward and Looking Back: Older Adults' Views of the Impacts of Stopping Driving

ABSTRACT This project aimed to identify the impact of driving cessation from the perspectives of older drivers and former drivers. Participants included 17 adults aged 65–88 years residing in a city in Northwestern Ontario, Canada. Using a semi-structured interview guide (with questions regarding mobility, personal impact, impact on others, engagement with life, and finances), two focus groups were held with nine current drivers, and one-on-one interviews were held with six former drivers and two current drivers. Two themes emerged concerning stopping driving. The first theme included discussions on experiencing lifestyle changes, relationship impacts, and emotional impacts. The second, the adjustment to stopping driving, included practical adaptations, and emotional responses such as appreciation, resistance, acceptance, and being positive. Although the impacts of stopping driving were substantial, there were few discrepancies between what was anticipated and what was experienced. This information could assist with developing interventions to ease the transition to former-driver status.