Age group differences in collision risk

Introduction

The purpose of the current study was to examine differences in factors associated with self-reported collision involvement of three age groups of drivers based on a large representative sample of Ontario adults. Method: This study was based on data from the CAMH Monitor, an ongoing cross-sectional telephone survey of Ontario adults 18 years and older from 2002 to 2005. Three age groups were examined: 18-34 (n = 1,294), 35-54 (n = 2,428), and 55+ (n = 1,576). For each age group sample, a logistic regression analysis was conducted of self-reported collision involvement in the last 12 months by risk factor measures of driving exposure (kilometers driven in a typical week, driving is stressful, and driving on busy roads), consuming five or more drinks of alcohol on one occasion (past 12 months), cannabis use (lifetime, and past 12 months), and driving after drinking among drinkers (past 12 months), controlling for demographics (gender, region, income, and marital status). Results: The study identified differences in factors associated with self-reported collision involvement of the three age groups of adult drivers. The logistic regression model for the youngest group revealed that drivers who reported that driving was stressful at least some of the time, drank five or more drinks on an occasion, and drove after drinking had an increased risk of collision involvement. For the middle age group, those who reported using cannabis in the last 12 months had significantly increased odds of reporting collision involvement. None of the risk factor measures showed significant associations with collision risk for older drivers (aged 55+). Impact: The results suggest potential areas for intervention and new directions for future research.     

Is there a link between motor vehicle collisions and being a cigarette smoker in Canada? Analysis of survey data from Ontario from 2002 to 2014

Objective: Although most research on drugs and driving has focused on the use of alcohol and cannabis, research that has been conducted on cigarette smoking and collisions has found that smokers have an increased collision involvement. Studies dating from 1967 through 2013 have shown a crude relative risk of about 1.5 among smokers compared to nonsmokers. In Canada, the association between smoking and collisions has not been recently investigated. Studies that have examined the association between smoking and collisions often did not control for all confounding factors, such as alcohol use and driving exposure, which have been associated with increased collision rates. Additionally, a number of these studies were examined in countries and at times when prevalence of smoking was much higher than is currently the case in Canada. The purpose of this research is to examine the association between self-reported current smoking and past-year collision involvement, controlling for confounding factors, in a large representative sample of adult drivers in Ontario, Canada, from 2002 and 2014.

Method: Data are based on the Centre for Addiction and Mental Health (CAMH) Monitor, an ongoing, rolling telephone survey of Ontario adults that provides epidemiological surveillance of indicators related to alcohol, tobacco, and other drug use, as well as physical and mental health. The survey uses random-digit-dialing methods via Computer-Assisted Telephone Interview, with response rates over 50%.

Results: Prevalence of self-reported collision involvement within the past year for 2002–2014 was 8.6% among those who currently smoke compared to 6.5% of nonsmokers. Logistic regression analysis, controlling for the potential confounding effects of sociodemographics, driving exposure measures, drinking frequency, and hazardous alcohol use, found that the overall odds for collision involvement in the preceding year among current smokers for 2002–2014 was 1.27 (95% confidence interval [CI], 1.06–1.53) times that of nonsmokers.

Conclusions: These findings indicate that despite a substantial reduction in overall prevalence of smoking in Canada, smokers still have a significantly increased odds of collision involvement, even when controlling for alcohol and exposure. Additionally, the results are consistent with the increased odds/risks of motor vehicle collisions found in other countries.     

Young drivers' determinants of driving under the influence of cannabis: Findings from the Youth Cannabis and Driving Survey (YouCanDS)

Introduction: Driving under the influence of cannabis (DUIC) is proven to increase the risk of collisions and is most common among young drivers (ages 16 to 24). However, little is known about the specific determinants of DUIC behavior among youth, which limits the capacity to develop evidence-based prevention and intervention efforts. This study developed and evaluated a youth DUIC questionnaire, which was used to establish the DUIC determinants of young drivers. Method: The questionnaire was based on the theoretical framework of general deterrence and general prevention. Data obtained included: demographics, past cannabis use and DUIC experiences, DUIC intention, experiences riding as a passenger with someone DUIC, knowledge and credibility of the law, attitudes towards DUIC, and social controls. The resulting questionnaire was validated for a sample of 426 young drivers in the province of Ontario, Canada. An ordinal regression was conducted to examine the relationships between questionnaire items and DUIC intention. Results: The questionnaire displayed good construct validity and internal consistency across four out of five domains (KMO and Cronbach α values ≥ 0.70). Of the 426 respondents (52.6% female), 356 (83.6%) reported previous cannabis use, with 296 (69.5%) doing so in the past year, and 142 (33.3%) reporting DUIC. Furthermore, 179 (42%) study participants indicated at least a slight chance of DUIC in the next year. The regression analysis identified six variables predictive of DUIC intention: past DUIC incidence, perceived percent of those convicted that receive the penalty, moral awareness, perceived dangerousness, minor accident risk, and vicarious punishment avoidance. Conclusions: Preventive efforts should emphasize these determinants when designing targeted strategies and interventions. Practical Applications: These efforts should focus on educating the dangers and risk of a vehicle collision, that law enforcement has the capacity to apprehend and appropriately punish individuals DUIC, and that DUIC is wrong and socially unacceptable.     

In-car cell phone use and hazards following hands free legislation

OBJECTIVE: A new law took effect in Finland at the beginning of 2003 which prohibits the handheld use of mobile phones while driving a motor vehicle. The purpose of this study was to assess the impact of the law on phone usage and self-reported safety during the first few months and 16 months later to determine whether the initial level of compliance with the law had been sustained. METHODS: Data were collected by Gallup home poll before (spring 2002) and after legislation took effect (spring 2003 and 2004). A representative sample of drivers who owned a cell phone (n = 836 to 966) was interviewed each time. On-road observations were also collected in four cities for 2003 and 2004. RESULTS: Just after the law, 97% of drivers were aware of the new hands free legislation. In sharp contrast to the pre-law rate of 16%, 43% reported not using the phone while driving immediately after the law and 41% one year later. The occasional users especially reduced their use of phones while driving. The law was correlated to reductions in self-reported handheld use of cell phones while driving, from 55.6% pre-law to 15.2% immediately after passage. In spite of this change, however, the hands free legislation did not reduce self-reported involvement of Finnish drivers in phone-related hazards. Handheld usage was still lower in 2004 than pre-law (20.0%), but the 32% increase from 2003 was significant. Observational data collected in Finland in 2003 and 2004 showed an even higher upward trend in handheld use (87% increase, from 3.1% to 5.8%; pre-law data were not available), and matched a similar increase reported by McCartt and Geary (2004) in their observational evaluation of New York's handheld mobile phone law. CONCLUSION: The self-reports indicate that the hands-free law reduced handheld phone use, among occasional users especially, but did not reduce phone-related hazards. The effect of the law on phone use substantially declined within one year.     

Teenage driving after using marijuana or drinking and traffic accident involvement

Anonymous random digit dialing telephone surveys of nearly 6000 16–19 year old respondents were conducted in Massachusetts and Upstate New York in 1979–1981. These surveys explored frequency of driving after using marijuana, driving after drinking, respondent accident involvement in the year prior to the interview, and a variety of other respondent characteristics. Frequency of driving after using marijuana and after drinking were each associated with greater accident involvement. To isolate the accident risk of driving after marijuana use, respondents who drove after drinking were excluded from a logistic regression analysis. This analysis also controlled for the distance respondents drove and several respondent demographic characteristics. Compared to respondents who did not drive after marijuana use, teenageers who drove after smoking marijuana on at least 6 occasions per month were 2.4 times more likely to be involved in traffic accidents. Those who drove after marijuana use on at least 15 occasions per month were 2.9 times more likely to have an accident.     

Associations between driving under the influence or riding with an impaired driver and future substance use among adolescents

Objective: Risky driving behaviors among adolescents, such as riding with a drinking or impaired driver (RWID) or driving while under the influence (DUI) of alcohol or drugs, are significant public health concerns. Few studies have examined associations of RWID and DUI with future substance use and problems after controlling for baseline substance use. Given that the DUI/RWDD event may be a teachable moment to prevent future consequences (e.g., when injured or arrested), it is important to understand how this risk behavior relates to subsequent use and problems. This study therefore examined characteristics of adolescents who reported DUI and RWID and assessed their risk of future alcohol and marijuana use and consequences 6 months later.

Methods: Participants were 668 adolescents aged 12 to 18 (inclusive) recruited at 1 of 4 primary care clinics in Pittsburgh and Los Angeles as part of a larger randomized controlled trial. They completed surveys about their health behaviors at baseline and 6 months after baseline. We examined baseline characteristics of adolescents who reported DUI and RWID and then assessed whether past-year DUI and RWID at baseline were associated with alcohol and marijuana use and consequences 6 months after baseline.

Results: Fifty-eight percent of participants were female, 56% were Hispanic, 23% were Black, 14% were White, 7% were multiethnic or other, and the average age was 16 years (SD?=?1.9). At baseline, participants who reported RWID or DUI were more likely to be older, report past-year use of alcohol and marijuana, and more likely to have an alcohol use disorder or cannabis use disorder versus those who did not report RWID or DUI, respectively. At 6-month follow-up and after controlling for baseline demographics and baseline alcohol use, RWID was associated with more frequent drinking episodes in the past 3 months and greater number of drinks in the past month when they drank heavily. DUI at baseline was associated with more frequent heavy drinking episodes and alcohol and marijuana consequences 6 months later.

Conclusions: RWID and DUI are significantly associated with greater alcohol and marijuana use over time. This study highlights that teens may be at higher risk for problem substance use in the future even if they ride with someone who is impaired. Prevention and intervention efforts for adolescents need to address both driving under the influence and riding with an impaired driver to prevent downstream consequences.     

Cell phone users, reported crash risk, unsafe driving behaviors and dispositions: a survey of motorists in Maryland

INTRODUCTION: The purpose of this investigation was to identify risky driving behaviors and dispositions that distinguish drivers who use a cell phone while operating a motor vehicle from non-cell phone using drivers. METHOD: Annual telephone surveys were used to identify drivers who reported using a cell phone while driving in the last month (n=1803) and were compared to those who said they did not use cell phones while driving (n=1578). RESULTS: Cell phone using drivers were more likely to report driving while drowsy, going 20 mph over the speed limit, driving aggressively, running a stop sign or red light, and driving after having had several drinks. They were also more likely to have had a prior history of citation and crash involvement than non-cell phone using drivers. Cell phone using drivers also reported they were less careful and more in a hurry when they drive than non-cell phone using drivers. CONCLUSION: Cell phone using drivers report engaging in many behaviors that place them at risk for a traffic crash, independent of the specific driving impairments that cell phone usage may produce. Strategies that combine coordinated and sustained enforcement activities along with widespread public awareness campaigns hold promise as effective countermeasures for these drivers, who resemble aggressive drivers in many respects.     

Self-reported driving under the influence of alcohol and cannabis among Ontario students: Associations with graduated licensing,risk taking,and substance abuse

Objective: This article describes the patterns of self-reported driving under the influence of alcohol (DUIA) and driving under the influence of cannabis (DUIC) among licensed Ontario students in 2009 and examines their associations with graduated licensing, risk taking, and substance use problems for understanding DUIA and DUIC behaviors. Ontario's graduated licensing system requires new drivers to hold a G1 license for a minimum of 8 months and a G2 license for a minimum of 12 months before a full and unrestricted G license can be obtained. Among other restrictions, G1 drivers must maintain a 0 blood alcohol content (BAC), have an experienced driver in the passenger seat, not drive on any high-speed expressways, and not drive between the hours of midnight and 5 a.m. A G2 license is more similar to a G license, with fewer restrictions.

Method: This study analyzed data from the 2009 Ontario Student Drug Use and Health Survey (OSDUHS). The OSDUHS is a biennial population-based survey of students (grades 7 to 12) in Ontario, Canada.

Results: The results showed that 16.3% of licensed students in Ontario reported DUIC and 11.5% reported DUIA during the past year. After controlling for the effect of age, type of license emerged as a robust predictor for both DUIA and DUIC behavior, because students with a G2 and full license were significantly more likely to report DUIA and DUIC than drivers with a G1 license. Multivariate analyses suggested that risk-seeking behaviors were more important for understanding DUIA behavior than for DUIC behavior. Elevated problem indicators for alcohol and for cannabis were associated with DUIA and DUIC, respectively.

Conclusions: Though much attention has been paid to drinking and driving among adolescents, this research shows that more Ontario students now report driving after cannabis use than after drinking alcohol. The results identify important correlates of both behaviors that may be useful for prevention purposes.     

Driving while impaired (DWI) by alcohol convictions among alcohol, cocaine, and cannabis clients in treatment

OBJECTIVE: Although studies have demonstrated that clients in treatment for alcohol abuse are more at risk of driving while impaired (DWI) by alcohol than normal licensed drivers from the general population, no research was found on DWI convictions among those in treatment for abusing cannabis or cocaine. The purpose of this article is to compare DWI convictions among clients in treatment for alcohol, cannabis, cocaine, or various combinations of these substances, compared to a matched population control group. METHOD: A stratified random sample of driver records was drawn from seven client groups who sought treatment in 1994 for alcohol, cannabis, cocaine, or any combination of these substances (n = 445). A random sample of drivers, frequency matched by age and sex (n = 566), served as control subjects. RESULTS: Logistic regression analysis, controlling for sex and age, was conducted to assess whether DWI convictions were elevated for each of the client groups, compared to controls. Two sets of analyses were conducted, before treatment (from 1985 to 1993) and after treatment (from 1995 to 2000). In the time period before treatment, every drug group except the "cannabis only" group had significantly more DWI convictions than controls (p < .05). In the period after treatment, the "alcohol only," "cocaine only," "alcohol and cocaine," and the "cocaine and cannabis" groups still had significantly more DWI convictions than controls (p < .05). CONCLUSION: The results show that DWI convictions are elevated among those who abused cocaine but not among those who abused cannabis. The results suggest that cross-addiction of alcohol and cocaine is common, and problematic drinking among cocaine clients can go undetected when clients are being diagnosed for treatment.     

Examining motor vehicle crash involvement and readiness to change on drinking and driving behaviors among injured emergency department patients

Objective: To measure the effect of motor vehicle crash (MVC) involvement and readiness to change drinking and driving behaviors on subsequent driving and drinking behaviors among injured emergency department (ED) patients who use alcohol at harmful levels.

Methods: This was a secondary analysis of a randomized controlled trial of injured ED patients who screened positive for harmful alcohol use, who at recruitment reported driving in the past 12 months and received at least one of the intended intervention sessions (brief behavioral intervention versus attention placebo control; N = 407). Outcome variables were as follows: (1) change in 6 impaired driving behaviors and (2) report of MVCs and traffic violations in the 12 months following recruitment; predictor variables were as follows: (1) treatment assignment, (2) MVC involvement at recruitment, and (3) baseline readiness to change alcohol use and drinking and driving.

Results: Modeling of change in the 6 impaired driving variables indicated that neither the recruitment visits being MVC related nor baseline readiness to change alcohol use and drinking and driving behaviors predicted greater changes in impaired driving over time. Baseline reports of past moving traffic violations and the ED visit being MVC related predicted a greater likelihood of each behavior at 12 months following study recruitment.

Conclusions: This study and others have demonstrated that ED patients with harmful alcohol use are willing to engage in behavioral interventions directed at changing risky behaviors. However, this study did not demonstrate that patients considered having the potential to be more engaged with the intervention because their ED visit was MVC related and/or they had expressed intent to change their risky alcohol use and drinking and driving behaviors were more likely to change these risky behaviors.     

Task-induced fatigue and collisions in adult drivers with attention deficit hyperactivity disorder

OBJECTIVE: This study compares collision involvement between adult drivers with attention deficit hyperactivity disorder (ADHD) and control participants in a simulation experiment designed to enhance the effects of fatigue. Because the effects of ADHD include difficulties in maintaining attention, drivers with ADHD were hypothesized to be more susceptible to the effects of fatigue while driving. METHODS: Data are drawn from a validated driving simulation study, portions of which were focused on enhancing the effects of fatigue. The simulator data are supplemented with written questionnaire data. Drivers with ADHD were compared with controls. RESULTS: The self-report data indicated that drivers with ADHD were more likely to report having been involved in an accident within the previous five years. Simulation data showed that time of day of participation in the experiment were significantly related to likelihood of collision, and that these effects were further exacerbated by ADHD status. Participants with ADHD were more likely than controls to be involved in a crash in the simulator regardless of time of day, but the effects were particularly pronounced in the morning, and the rate of increase in accident involvement from the late afternoon into the evening was greater among participants with ADHD. No differences in self-reported sleep patterns or caffeine use were found between participants with ADHD and controls. CONCLUSIONS: The results suggest that drivers with ADHD became fatigued more quickly than controls. Such drivers thus face greater risk of involvement in accidents on highways or open roadways where the visual and task monotony of the environment contribute to greater driver fatigue.     

MaryPODS revisited: updated crash analysis and implications for screening program implementation

PROBLEM: Due to the relative scarcity of crashes, there has consistently been a problem with analyses that use crashes as a criterion measure in their analyses. METHOD: Previous analyses of the relationships between functional capacity measures and at-fault crash involvement for older drivers as reported in the NHTSA Model Driver Screening and Evaluation Program Final Technical Report have been updated to include one additional year of driving experience. Eighteen new at-fault crashes involving drivers who previously had no crash involvement were recorded for the Maryland Motor Vehicle Administration (MVA) test sample during this interval. The method of odds ratio (OR) calculation was used to examine the relationships between functional status predictors and the most salient among the safety outcome measures identified in the Maryland research. Peak valid OR values for the prior and current analyses were contrasted, and the stability of candidate pass-fail cut-points for each predictor relative to values identified in the Final Technical Report was examined. RESULTS: Results indicate that the predictive value of functional tests appears to decrease over time, particularly for the perceptual-cognitive measures. IMPACT ON INDUSTRY: The impact of these findings on programs and policies is to underscore a need for periodic reevaluation, spaced at the shortest practical intervals but not more than 2 years apart, in order for functional capacity screening to be applied effectively by licensing authorities, health care professionals, and others to reduce personal risk and enhance public safety.     

Marijuana use and driving in Washington State: Risk perceptions and behaviors before and after implementation of retail sales

Objective: Washington is among the first states to legalize recreational use of marijuana. This study examined marijuana use and risk perceptions before and after retail sales of recreational marijuana began in July 2014, the relationship between risk perceptions and marijuana use, and the relationship between self-reported marijuana use and drug test results.

Methods: Roadside surveys were conducted in 3 waves: June 2014, the month before retail sales of marijuana began; 5–6 months later (November–December 2014); and 1 year later (June 2015). A total of 2,355 drivers completed a marijuana questionnaire about their past and current marijuana use and perceived risks associated with driving after using marijuana. Data collection also included biological specimens (oral fluid and/or blood for marijuana testing and breath for alcohol testing). Drivers who tested positive for delta-9-tetrahydrocannabinol or 11-hydroxy-delta-9-tetrahydrocannabinol in oral fluid or blood were defined as THC-positive.

Results: The proportion of drivers who reported recent marijuana use was similar across the 3 surveys. However, the proportion of THC-positive daytime drivers increased from 8% before retail sales to 23% 6 months after retail sales; this proportion did not change among nighttime drivers (19 and 20%). Drivers’ perceived risk of impairment by marijuana and perceived risk of being arrested for marijuana-impaired driving were similar before and after retail sales. The odds of being THC-positive were 40% lower among drivers who perceived that marijuana was very likely to impair driving, compared to other drivers. Drivers’ perceived risk of being arrested for marijuana-impaired driving was not predictive of THC-positive driving.

Conclusions: The prevalence of daytime THC-positive drivers increased substantially a few months after retail sales of marijuana were legal. Daytime and nighttime prevalence of THC-positive drivers was similar after retail sales. This pattern differs from that typically found for alcohol use, which is consistently higher among drivers at nighttime, compared to daytime. Reports of marijuana use were not always consistent with drug test results, which suggests that comparisons of self-reported marijuana use before and after legalization could be biased. This study examined marijuana use and risk perceptions over the course of 1 year. However, law changes may influence cultural norms gradually over a longer period of time. Future studies should continue to monitor marijuana use over time, as well as identify ways to determine whether drivers are impaired by marijuana.     

Relationships between frequency of driving under the influence of cannabis,self-reported reckless driving and risk-taking behavior observed in a driving simulator

IntroductionThe role of cannabis consumption in traffic crashes is unclear and the causal link between cannabis and collisions is still to be demonstrated. While cannabis use is very likely to impair driving ability, there is as yet no overwhelming evidence that cannabis use in isolation contributes more to collisions than other characteristics inherent to cannabis users. As noted in a growing body of literature, individuals driving under the influence of cannabis (DUIC) seem to exhibit a general reckless driving style putting them at higher risk to be involved in traffic crashes.MethodThis study aims at investigating the relationship between self-reported DUIC and reckless driving by means of self-reported measures and direct observations made in a driving simulator. Participants (n = 72) were required to be between 18 and 25 years of age, to hold a valid driver's license, and to drive at least twice a week. They completed standard driving simulation tasks recreating everyday on-road trivial conditions.ResultsResults show that people admitting that they commit more real-life dangerous driving behaviors reached higher maximum speed and demonstrated more reckless driving behaviors on the driving simulation tasks. Self-reported DUIC is associated with a risky driving style including a broad range of reckless on-road behaviors and support the problem driving behavior theory. Moreover, beyond confounding factors, both self-report DUIC and observed dangerous behaviors are associated with real-life traffic violations.Practical applicationsSince DUIC appears to be related to an overall reckless style of driving, it is proposed that public safety policies should be more holistic, simultaneously targeting multiple on-road dangerous behaviors for intervention.     

The role of drug and alcohol use and the risk of motor vehicle crashes in Shiraz,Iran, 2014: A case–crossover study

Background: Traffic accidents and traffic-related injuries and mortality have become a major public health concern in Iran. This study aimed to examine the role of drug and alcohol use in motor vehicle accidents in Iran.

Methods: This case–crossover study was conducted on 441 drivers who survived a road traffic crash and were taken to the emergency department of Shahid Rajaee trauma hospital in Shiraz, southern Iran. Data were collected using checklists that included demographic characteristics and drug and alcohol use prior to driving. Alcohol and drug use was identified through self-report, and cannabis, morphine, and methamphetamine urine tests were used to confirm drug abuse among drivers.

Results: In total 17.9% of drivers reported using drugs (cannabis, opium, or metamphetamine) and 8.84% of drivers reported consuming alcohol prior to the collision. The crude odds ratios (ORs) for having a crash for opium, cannabis, and metamphetamine were 1.94 (95% interval confidence [CI], 1.11–3.38), 2.37 (95% CI, 1.03–5.42), 5.5 (95% CI, 1.21–24.81), respectively, and for all drugs was 3.83 (95% CI, 2.28–6.43). The OR for alcohol was 3.5 (95% CI, 1.73–7.06) based on self-report.

Conclusion: Drug and alcohol use are increasing the risk of traffic crashes in Iran. Risk-reducing programs must be designed and implemented.     

Attitudes toward mandatory ignition interlocks for all offenders convicted of driving while intoxicated

Introduction: Ignition interlocks are effective in reducing alcohol-impaired driving recidivism for all offenders, including first-time offenders. Despite their effectiveness, interlock use among persons convicted of driving while intoxicated from alcohol (DWI) remains low. This cross-sectional survey of U.S. adults assessed public support for requiring ignition interlocks for all convicted DWI offenders including first-time offenders. The goal was to update results from a similar 2010 survey in light of new state requirements and increased interlock installations. Methods: Questions were included in the Porter Novelli FallStyles survey, which was fielded from September 28 to October 16, 2015. Participants were the 3,536 individuals who provided an opinion toward requiring ignition interlocks for all offenders. For analyses, opinion toward requiring interlocks for all offenders was dichotomized into ‘agree’ and ‘neutral/disagree.’ To handle missing data, 10 imputed datasets were created and pooled using fully conditional specification (FCS). Results: Fifty-nine percent of adults supported requiring interlocks for all DWI offenders. Multivariate analysis revealed that persons who did not report alcohol-impaired driving (AID) were 60% more likely to support requiring interlocks than those who reported AID. Having heard of interlocks also increased support. Support was generally consistent across demographic subgroups. Conclusions: Interlocks for all offenders have majority support nationwide in the current survey, consistent with previous reports. Support is lowest among those who have reported alcohol-impaired driving in the past 30 days. These results suggest that communities with higher levels of alcohol-impaired driving may be more resistant to requiring ignition interlocks for all convicted DWI offenders. Future studies should examine this association further. Practical applications: These results indicate that the majority of adults recognize DWI as a problem and support requiring interlocks for all offenders.     

Analysis of effects of driver’s evasive action time on rear-end collision risk using a driving simulator

Introduction: Driver’s evasive action is closely associated with collision risk in a critical traffic event. To quantify collision risk, surrogate safety measures (SSMs) have been estimated using vehicle trajectories. However, vehicle trajectories cannot clearly capture presence and time of driver’s evasive action. Thus, this study determines the driver’s evasive action based on his/her use of accelerator and brake pedals, and analyzes the effects of the driver’s evasive action time (i.e., duration of evasive action) on rear-end collision risk. Method: Fifty drivers’ car-following behavior on a freeway was observed using a driving simulator. An SSM called “Deceleration Rate to Avoid Crash (DRAC)” and the evasive action time were determined for each driver using the data from the driving simulator. Each driver tested two traffic scenarios – Cars and Trucks scenarios where conflicting vehicles were cars and trucks, respectively. The factors related to DRAC were identified and their effects on DRAC were analyzed using the Generalized Linear Models and random effects models. Results: DRAC decreased with the evasive action time and DRAC was closely related to drivers’ gender and driving experience at the road sections where evasive action to avoid collision was required. DRAC was also significantly different between Cars and Trucks scenarios. The effect of the evasive action time on DRAC varied among different drivers, particularly in the Trucks scenario. Conclusions: Longer evasive action time can significantly reduce crash risk. Driver characteristics are more closely related to effective evasive action in complex driving conditions. Practical Applications: Based on the findings of this study, driver warning information can be developed to alert drivers to take specific evasive action that reduces collision risk in a critical traffic event. The information is likely to reduce the variability of the driver’s evasive action and the speed variations among different drivers.     

How do drivers avoid collisions? A driving simulator-based study

Introduction: Drivers' collision avoidance performance in an impending collision situation plays a decisive role for safety outcomes. This study explored drivers' collision avoidance performances in three typical collision scenarios that were right-angle collision, head-on collision, and collision with pedestrian. Method: A high-fidelity driving simulator was used to design the scenarios and conduct the experiment. 45 participants took part in the simulator experiment. Drivers' longitudinal/lateral collision avoidance performances and collision result were recorded. Results: Experimental results showed that brake only was the most common response among the three collision scenarios, followed by brake combining swerve in head-on and pedestrian collision scenarios. In right-angle collision scenario with TTC (time to collision) largest among three scenarios, no driver swerved, and meanwhile drivers who showed slow brake reaction tended to compensate the collision risk by taking a larger maximum deceleration rate within a shorter time. Swerve-toward-conflict was a prevalent phenomenon in head-on and pedestrian collision scenarios and significantly associated with collision risk. Drivers that swerved toward the conflict object had a shorter swerve reaction time than drivers that swerved away from conflict. Conclusions: Long brake reaction time and wrong swerve direction were the main factors leading to a high collision likelihood. The swerve-toward-conflict maneuver caused a delay in brake action and degraded subsequent braking performances. The prevalent phenomenon indicated that drivers tended to use an intuitive (heuristic) way to make decisions in critical traffic situations. Practical applications: The study generated a better understanding of collision development and shed lights on the design of future advanced collision avoidance systems for semi-automated vehicles. Manufactures should also engage more efforts in developing active steering assistance systems to assist drivers in collision avoidance.