Relationship between Walking and Driving, and Cognitive Functioning Common to Both Modes of Mobility, in Healthy Older Adults.

INTRODUCTION: Driving and walking, the two main modes of mobility, require numerous common skills in the motor, sensory, and cognitive domains that deteriorate with age. The objective of this study was to investigate the relationship between walking and driving in healthy older drivers and to determine whether certain cognitive processes are involved in both modes of mobility. METHOD: Seventy-six older drivers from the Safe Move cohort were assessed in the following three domains: (1) cognition, using parts A and B of the Trail Making Test (TMT), the digit symbol substitution test (DSST), the Stroop test, and the Digit span; (2) gait, using a dual-task (DT) paradigm with a counting task; and (3) driving, assessed via a 40-50 min on-road test. Analyses were also performed on 2 subgroups: young-old (70-74 years old; n = 43) and old-old (≥75 years; n = 33). RESULTS: Four significant correlations were found across the whole sample between gait performance under DT conditions and driving scores. One correlation was also found in old-old adults. None were found in young-old adults. Furthermore, several cognitive measures were significantly correlated to both modes of mobility: TMT-A and B completion time in the whole sample, and DSST performance in the whole sample and old-old adults. DISCUSSION/CONCLUSION: Walking in complex conditions and on-road driving performance are closely related in healthy older drivers. Visuospatial attention, processing speed, and executive function are crucial and common cognitive processes to both modes of mobility in this population. Impairment in these cognitive functions should thus alert health professionals as it can quickly lead to mobility disorders, loss of autonomy and social isolation. Developing specific preventive programs and mobility support systems for healthy older adults is also crucial.

Chronic medical conditions and their association with crash risk and changes in driving habits: a prospective study of the GAZEL cohort.

OBJECTIVES: To assess crash risk and driving habits associated with chronic medical conditions among drivers entering old age. DESIGN: Prospective cohort study. SETTING: French cohort GAZEL. PARTICIPANTS: 12 460 drivers in the analysis of road traffic crash, among whom 11 670 completed the follow-up period (2007-2014). We assessed driving cessation among 11 633 participants over the same period, and mileage and driving avoidance among the 4973 participants who returned a road safety questionnaire in 2015. MAIN OUTCOME MEASURES: Yearly occurrence of at least one road crash as a driver; time to driving cessation; mileage; driving avoidance: at night, with bad weather, in heavy traffic, with glare conditions, over long distances. RESULTS: Several potentially risky conditions (angina, myocardial infarction, coronary disease; stroke; nephritic colic, urinary stones; glaucoma) were associated with lower mileage and/or driving avoidance and did not increase crash risk. Neither driving avoidance nor lower mileage was found for other conditions associated with an increased crash risk: hearing difficulties (adjusted OR 1.19, 95% CI 1.06 to 1.34); joint disorders (1.17, 95% CI 1.06 to 1.30). Depression, anxiety and stress was associated with an increased crash risk (1.23, 95% CI 1.01 to 1.49) despite increased driving avoidance. Parkinson's disease was associated with driving cessation (adjusted HR 32.61, 95% CI 14.21 to 65.17). CONCLUSIONS: Depending on their condition, and probably on the associated risk perception, drivers entering old age report diverse driving habits. For example, hearing difficulties is a frequent condition, rarely considered a threat to road safety, and nonetheless associated with an increased crash risk.

Barriers and facilitators to social participation after driving cessation among older adults: A cohort study.

BACKGROUND: Driving cessation is a challenging transition for older drivers. It is indeed often associated with reduced mobility, loss of autonomy and poor quality of life, as in individuals with acquired disabilities. We examined factors that inhibit or facilitate out-of-home occupations after driving cessation (shopping, visiting/helping friends/family, leisure, and associative activities) in older adults, with particular focus on the role of anticipation. METHODS: This longitudinal study was conducted with the SAFE MOVE cohort (n=1014 drivers aged≥70 years). Socio-demographic, health, cognitive, mobility and out-of-home occupations data were collected at home at baseline and by a postal questionnaire at 2-year follow-up. RESULTS: In total, 48 (5%) participants stopped driving between baseline and follow-up, at a mean age of 81.8 years; 71% of drivers who stopped reported that driving cessation affected their out-of-home occupations. Participation in social occupations started to decline before driving cessation. Retired drivers were older, had poorer health, poorer cognitive abilities, drove less at baseline but used more public transportation than active drivers. As compared with participants who did not consider driving cessation at baseline, those who did were more likely to expect a better quality of life in the event of driving cessation and to use public transportation at baseline and follow-up despite their older age and poorer health. CONCLUSION: Some factors associated with reduced social participation and driving cessation are inevitable, such as health status. However, other factors may facilitate maintenance of social participation, including anticipation of driving cessation and mobility habits. Our findings highlight the need for appropriate interventions that are widely available to older drivers before driving cessation occurs and for public policy actions facilitating alternative transport systems.

Relationships Between Cognitive and Driving Self-awareness in Older Drivers.

OBJECTIVES: Many older drivers incorrectly estimate their driving ability. The present study aimed to determine whether, and if so, to what extent unawareness of cognitive abilities affects self-awareness of driving ability. METHOD: Two successive studies were conducted in older drivers. A cohort study investigated cognitive self-awareness and an experimental study examined driving self-awareness. In each one, self-awareness was assessed by cross-analyzing objective (respectively Trail-Making Tests A and B and the Digit Symbol Substitution Test and driving performance of on-road assessment) and subjective data (responses about everyday cognitive skills and driving ability). Older drivers were then classified as being over-, correct, or underestimators. The 3 cognitive and driving self-awareness profiles were then cross-analyzed. RESULTS: In the cohort study, 1,190 drivers aged 70 years or older were included. The results showed that 42.7% of older drivers overestimated their cognitive ability, 42.2% estimated it correctly, and 15.1% underestimated it. The experimental study included 145 participants from the cohort. The results showed that 34% of participants overestimated, 45% correctly estimated, and 21% underestimated their driving ability. There was a significant relationship between cognitive and driving self-awareness profiles (p = .02). This overlap was more marked in overestimators. DISCUSSION: Significant overlap between cognitive and driving self-awareness provides useful and new knowledge about driving in the aging population. Misestimation of cognitive ability could hamper self-awareness of driving ability, and consequently self-regulation of driving. It is now crucial to develop measures that promote self-awareness of ability.

Naturalistic Driving Study Investigating Self-Regulation Behavior in Early Alzheimer's Disease: A Pilot Study.

BACKGROUND: Because cognitive processes decline in the earliest stages of Alzheimer's disease (AD), the driving abilities are often affected. The naturalistic driving approach is relevant to study the driving habits and behaviors in normal or critical situations in a familiar environment of participants. OBJECTIVE: This pilot study analyzed in-car video recordings of naturalistic driving in patients with early-stage AD and in healthy controls, with a special focus on tactical self-regulation behavior. METHODS: Twenty patients with early-stage AD (Diagnosis and Statistical Manual of Mental Disorders, Fourth Edition [DSM-IV] criteria), and 21 healthy older adults were included in the study. Data collection equipment was installed in their personal vehicles. Two expert psychologists assessed driving performance using a specially designed Naturalistic Driving Assessment Scale (NaDAS), paying particular attention to tactical self-regulation behavior, and they recorded all critical safety events. RESULTS: Poorer driving performance was observed among AD drivers: their tactical self-regulation behavior was of lower quality. AD patients had also twice as many critical events as healthy drivers and three times more "unaware" critical events. CONCLUSION: This pilot study used a naturalistic approach to accurately show that AD drivers have poorer tactical self-regulation behavior than healthy older drivers. Future deployment of assistance systems in vehicles should specifically target tactical self-regulation components.

Gender effect on driving cessation in pre-dementia and dementia phases: results of the 3C population-based study.

OBJECTIVES: Aging entails deterioration in sensory, physical, and cognitive functions, raising doubt in the driving capacity of older drivers, especially when the deficits are severe, as in dementia. Many older drivers, especially women, adapt their driving habits in order to compensate for these deficits and eventually stop driving. The present prospective study assessed driving cessation in men and women throughout the dementia process, including a 2-year pre-dementia phase. METHODS: The study was based on a three-city cohort of subjects who were aged 65 years and older in 2000 and followed for more than 10 years. Active dementia detection was conducted at each follow-up. The probability of driving cessation was assessed in men and women during the 2-year pre-dementia phase and until 5 years after diagnosis. RESULTS: In the 2-year pre-dementia phase, both men and women ceased driving earlier than drivers with no central nervous system pathology (p < 0,001), and women ceased driving earlier than men. A total of 45% of men and 74% of women had already ceased driving at dementia diagnosis. In contrast, the probability of cessation within 3 years after diagnosis was similar between men and women. CONCLUSION: The study showed that, in this French urban population, few demented drivers, especially women, were still driving after diagnosis. Those who continued to drive 3 years after the diagnosis all had Alzheimer-type dementia. There is certainly a need for physicians to help these drivers to adapt their driving activity to their deficits and to prepare them to stop driving. Copyright © 2016 John Wiley & Sons, Ltd.

The role of navigation instruction at intersections for older drivers and those with early Alzheimer's disease.

AIMS: Our purpose was to explore the effect of navigation instruction on older drivers' driving performance at left turn intersections. Left turns at intersections are particularly complex because they require many perceptive and cognitive abilities under considerable time pressure. METHODS: Fifty-four participants were recruited: 18 drivers with early-stage Alzheimer's disease (AD), 18 neurologically healthy older drivers and 18 younger individuals. Various cognitive processes were measured, and 9 left turn maneuvers with or without navigation instruction were evaluated during an in-traffic road test. The psychomotor, planning and decision-making components involved in left turn were also analyzed closely. RESULTS: Only older drivers (both healthy drivers and those with AD) were negatively affected by navigation instruction during the maneuver. The planning and decision-making components were more likely to be affected by the navigation instruction. CONCLUSION: This finding highlights the importance of carefully considering the use of navigation instructions when developing navigation systems. Adapting this instruction is necessary to simplify our understanding of the real-world driving environment and to avoid increasing the cognitive load of older drivers.

[Car driving, cognitive aging and Alzheimer disease]. / Conduite automobile, vieillissement cognitif et maladie d'Alzheimer.

Older drivers are more numerous on the roads. They are expert drivers, but with increasing age certain physiological changes can interfere with driving, which is a complex activity of daily living. Older drivers are involved in fewer accidents than younger drivers, but they have a higher accident rate per kilometer driven. The elderly are heavily represented in the balance sheet of road deaths, being motorists or pedestrians. This high mortality is largely explained by their physical frailty. In the presence of deficits, self-regulation of driving habits, changes/reductions or stopping in driving activity occur in the elderly. But cognitive deficits are associated with an increased risk of accidents. Among drivers with Alzheimer's disease, there is a heterogeneity of driving ability, making difficult the advisory role of a physician for driving. A protocol for physicians was developed to assess cognitive impairments that may affect driving in an elderly patient. The car plays an important role in the autonomy of the elderly and patient advice on stopping driving should take into account the risk/benefit ratio.

Automobile driving in older adults: factors affecting driving restriction in men and women.

OBJECTIVES: To identify factors associated with driving restriction in elderly men and women. DESIGN: Prospective cohort study of French drivers from 2003 to 2009. SETTING: The Three-City Cohort of Bordeaux, a prospective study of 2,104 people aged 65 and older. PARTICIPANTS: Five hundred twenty-three drivers with a mean age of 76 (273 male, 250 female). MEASUREMENTS: Sociodemographic characteristics, driving habits, health variables, cognitive evaluation and dementia diagnosis. Predementia was defined as no dementia at one follow-up and dementia at the next follow-up. RESULTS: Over the 6-year period, 54% of men and 63% of women stopped driving or reduced the distance they drove. Predementia, Parkinson's disease, older age, and a high number of kilometers previously driven were common restriction factors in both sexes. Prevalent dementia, depressive symptomatology, a decline in one or more instrumental activities of daily living, and poor visual working memory were specific factors in men. In women, low income, fear of falling, slow processing speed, and severe decline in global cognitive performance all affected driving restriction. CONCLUSION: Older women restricted their driving activity more than older men, regardless of the number of kilometers previously driven, physical health, and cognitive status. Factors affecting driving restriction differed according to sex, and women were more likely to stop driving than men in the period preceding a dementia diagnosis.

Why drivers start drinking and driving--a prospective study over a 6-year period in the GAZEL cohort.

AIMS: To estimate the frequency with which a group of formerly safe drivers adopt driving while alcohol-intoxicated (DWI), and to determine the factors associated with DWI adoption. METHODS: Participants were current employees or recent retirees of the French national electricity and gas company. An annual cohort questionnaire that includes two questions about overall alcohol consumption is sent each year to participants. A Driving Behaviour and Road Safety (DBRS) questionnaire was administered in 2001, 2004 and 2007. Only drivers who participated in the 2001 survey received the 2004 and 2007 questionnaires. RESULTS: More than 462 participants ceased DWI between 2001 and 2007, while 511 adopted this behaviour for the first time. Multivariate analysis showed that the risk of adopting DWI was associated with male gender and with several changes over the preceding years: increased alcohol consumption, increased number of close friends, decreased number of close relatives and decreased attitudes in favour of strict enforcement/regulations. CONCLUSION: A large number of offenders stopped DWI between 2001 and 2007, concomitantly with an increased crackdown on road violations in France. But this success was compromised by the occurrence of new drunk drivers. Preventive strategies should target factors that facilitate DWI adoption-in particular, increased alcohol consumption and low acceptance of law enforcement initiatives.

The Wechsler Digit Symbol Substitution Test as the best indicator of the risk of impaired driving in Alzheimer disease and normal aging.

AIMS: Our purpose was to identify cognitive tools associated with unsafe driving among elderly drivers of varying cognitive levels. METHODS: Twenty drivers with early-stage dementia of the Alzheimer type and 56 nondemented drivers aged 65-85 were recruited. Various cognitive processes were measured and unsafe driving was evaluated during an in-traffic road test with 3 different indicators and a composite indicator. RESULTS: The Wechsler Digit Symbol Substitution Test score was the best cognitive measure to detect unsafe drivers using the composite driving indicator. CONCLUSION: The Digit Symbol Substitution Test may be used by physicians for the evaluation and follow-up of older patients, with or without Alzheimer-type dementia, as a screening tool of unsafe driving.

Failure to reduce drinking and driving in France: a 6-year prospective study in the GAZEL cohort.

AIM: An unprecedented decline in alcohol consumption and road mortality has been observed recently in France, but it is still unclear whether or not these changes affected driving while alcohol-intoxicated (DWI). The objective of the study was to estimate prospectively trends of excessive speed on the roads, alcohol consumption and DWI between 2001 and 2007 in a large cohort of experienced drivers. METHODS: Participants were current employees or recent retirees of the French national electricity and gas company, who volunteered to participate in a research cohort established in 1989 under strict conditions of anonymity. An annual cohort questionnaire is sent to participants that includes two questions about overall alcohol consumption. In 2001 and 2007, 10,684 participants reported their driving behaviours using the same self-administered questionnaire. RESULTS: Between 2001 and 2007, the proportion of participants (n = 10,684) who reported having driven at speeds at least 20 km/hour above the limit decreased from 23.7% to 4.1% in built-up areas (P < 0.001), from 34.3% to 9.3% on rural roads (P < 0.001) and from 24.3% to 2.7% on highways (P < 0.001). Regular and non-regular excessive alcohol consumption decreased from 22.7% to 19.7% and from 18.0% to 14.9%, respectively, whereas DWI increased from 22.9% to 25.3% over the same period (P < 0.001). CONCLUSIONS: A recent crackdown on road violations by the French government has failed to deter DWI. Given that DWI seems to be a sporadic and rarely punished behaviour, its prevention requires more coercive measures, such as using a breath alcohol ignition interlock device.

Road casualties and changes in risky driving behavior in France between 2001 and 2004 among participants in the GAZEL cohort.

OBJECTIVES: We investigated behavioral changes in a large cohort of drivers to identify underlying causes of the decline in road casualties in France. METHODS: In 2001 and 2004, 11,240 participants used self-administered questionnaires to report attitudes toward road safety and driving behaviors. Injury road traffic collisions were recorded from 2001 to 2005 through the cohort's annual questionnaire. RESULTS: Between 2001 and 2004, speeding and cell phone use decreased concomitantly with a decrease in injury road traffic collision rates among participants. Reported driving while sleepy remained unchanged and driving while alcohol intoxicated was reported by a higher proportion in 2004 than in 2001. Decreases in speeding between 2001 and 2004 were strongly linked with positive attitudes toward road safety in 2001. CONCLUSIONS: In this cohort, speeding and using a cell phone while driving decreased over the 2001 to 2004 period concomitantly with increases in traffic law enforcement and a dramatic decline in road mortality in France. However, the deterrent effect of traffic enforcement policies may have been reduced by negative attitudes toward traffic safety and having had a history of traffic penalty cancellations.

Impact of retirement on risky driving behavior and attitudes towards road safety among a large cohort of French drivers (the GAZEL cohort).

OBJECTIVES: This study investigated changes in driving behavior and attitudes towards road safety, following retirement, in a large cohort of road users. METHODS: In 2001, 14 226 participants of the GAZEL cohort in France reported their attitudes towards road safety and driving behavior using a self-administered driving behavior and road safety questionnaire. In 2004, 82% of the group (N=11 706) responded to the same questionnaire. Two complementary logistic regression analyses were performed to assess the association of (i) retirement with change in safe driving behavior and attitudes towards road safety between 2001 and 2004 and (ii) time since retirement with risky driving behavior and negative attitudes towards road safety in 2001. RESULTS: Among the participants who were active in 2001 (N=3927), those retiring between 2001 and 2004 (66%) were more likely to have discontinued sleepy driving [adjusted odds ratio (aOR) 2.12, P<0.001] and phone use while driving (aOR 1.74, P=0.006) than those who remained professionally active. The second analysis showed that the likelihood of sleepy driving and phone use while driving decreased soon after retirement, whereas that of speedy driving decreased over a longer interval. Retirement had no influence on driving while intoxicated or attitudes towards road safety. CONCLUSIONS: The results suggest that any professional activity may account for some risky road behavior. As work-related road traffic accidents are responsible for one out of every four road casualties in France, the monitoring and prevention of sleepy driving and phoning while driving among workers should be further considered.

Tiring job and work related injury road crashes in the GAZEL cohort.

The objective was to describe at-work and commuting crashes occurring in a cohort of French employees and to investigate occupational risk factors. The subjects were employees of the French national electricity and gas companies, Electricité de France and Gaz de France (EDF-GDF), who volunteered to join a research cohort (the GAZEL cohort which included 20,625 participants in 1989). Only crashes with injuries were considered. Crashes for the periods 1989--2001 were recorded together with the type of journey (commuting, work, private), the type of road-user, self-estimated responsibility, and injuries sustained by the subject. Annual incidences for gender/age groups and socio-occupational groups were computed for each of the two types of work related crashes. Occupational risk factor analyses were conducted using a Cox proportional hazards regression model with time-dependent covariates adjusting for the main confounders. A total of 146,285 person years at work were observed. Two indicators of self-reported work fatigue were associated with the occurrence of at-work crashes: "nervously tiring work" for males (RR=1.6, 95% CI [1.1; 2.3]), sustained standing for females (RR=3.0, 95% CI [1.0; 8.4]), adjusting for health status, location of residence, type of family, transport mode and mileage. As regards crashes while commuting, a self-reported uncomfortable position at work was a risk factor among women (RR=1.9, 95% CI [1.1; 3.3]). On the other hand, these occupational factors were not linked to road crashes in private trips. Work related road crashes seem then to be a matter for a specific prevention. Preventing employees from becoming exhausted should be considered as the first way to initiate such a prevention.

Driving cessation and self-reported car crashes in older drivers: the impact of cognitive impairment and dementia in a population-based study.

The complexity of driving activity has incited numerous developed countries to initiate evaluative procedures in elderly people, varying according to first evaluation age, frequency, and screening tools. The objective of this paper is to improve the knowledge of the driving cessation process regarding factors associated with crash involvement. Driving cessation and self-reported crashes during the past 5 years were analyzed with multivariate models, in a cross-sectional study including a population-based sample of 1051 drivers aged 65 years and more. Visual trouble, Parkinson disease, dementia, and stroke history were associated with driving cessation. Future dementia was associated with self-reported crashes only. Attentional and executive deficits were associated with both outcomes. The detection of attentional and executive deficits should be included in driving evaluation procedures to improve awareness of these deficits by older drivers.

Actual incidences of road casualties, and their injury severity, modelled from police and hospital data, France.

BACKGROUND: Nation-wide road casualty figures usually come from police data. In France, as in many developed countries, the reporting of fatalities is almost complete but the reporting of non-fatal casualties is rather low. It is moreover strongly biased. Valid estimates are needed. METHODS: Using the capture-recapture method on police data and on a road trauma registry covering a large county of 1.6 million inhabitants, we estimate police under-reporting correction factors that account for unregistered casualties. These correction factors are then applied to the nation-wide police data, with standardization on under-reporting bias factors. RESULTS: In 2004, whereas the police report 108,727 non-fatally injured, the estimation yields 400,200. Over the 1996-2004 study period, the average annual estimated incidence is 871/100,000 for all injured (3.4 times the police incidence), 232/100,000 for hospitalized, 103/100,000 for seriously injured (2.2 times the police incidence) and 12.6/100,000 for casualties with long-term major impairment. The incidence of seriously injured (NISS 9+) is 11.3/100,000 for pedestrians, 9.5/100,000 for cyclists, 36.3/100,000 for motorized two-wheel users and 42.5/100,000 for car users. CONCLUSIONS: The estimated incidences are much higher than the police-based ones. This changes the scale of the road injuries issue. The risk of suffering a major impairment from a road crash is equal to the risk of being killed. Motorized two-wheel users experience a large burden of traffic casualties, much larger than that indicated by police data. The approach used can be reproduced in other countries, if an additional medical registration exists.

The impact of driver age on lost life years for other road users in France: A population based study of crash-involved road users.

BACKGROUND: One of the concerns in road safety is the threat older drivers may pose to other road users. Using the rate of lost life years, the present study provides a public health approach to quantify this potential threat. METHODS: A total of 1570686 motorised vehicle drivers or motorcycle riders and 652246 non-drivers, i.e. vehicle passengers, pedestrians and cyclists involved in injury crashes in France between 1996 and 2004, were included in a population based cross-sectional study. Fatality rates and rate of lost life years for each crash-involved driver age class were calculated for the drivers themselves and for other road users. RESULTS: The study has shown a significant reduction in the rate of lost life years for crash-involved other road users (whether passengers, pedestrians, cyclists or opposing drivers) as driver age increases. Other road users lost half as many years of life when involved in crashes with drivers aged over 85 than with drivers under 65 (1.26 and 2.32 per 100 expected remaining life years, respectively). CONCLUSION: Our findings suggest that among road users involved in injury crashes, older drivers are less dangerous for the other road users. By attributing other road users' lost life years to each driver age, this study represents a new contribution to the debate about ageing and road safety.

Attitudes associated with behavioral predictors of serious road traffic crashes: results from the GAZEL cohort.

OBJECTIVES: To test the hypothesis that behavioral predictors of serious road traffic crashes (RTC) are correlated with unfavorable attitudes towards traffic safety. DESIGN: Prospective and cross-sectional cohort study. SETTING: France PARTICIPANTS: 13,447 of the 19,894 living members of the GAZEL cohort, workers and recent retirees of a French national utility company followed up since 1989. MAIN OUTCOMES MEASURES: Driving behavior and attitudes towards traffic safety in 2001 by questionnaire. Serious RTCs were recorded over the subsequent 3 years using the cohort annual questionnaire. Behavioral predictors of serious RTCs were assessed using generalized linear Poisson regression models with time-dependent covariates. Factor scores extracted from the first four attitudinal factors of principal component analysis were saved and then regressed on behavioral predictors as independent variables. RESULTS: After controlling for potential confounders, the best predictors of serious RTCs were: "exceeding speed limits on rural roads", "risky use of cellular phone", and "sleepy driving". The adjusted rate ratio ranged from 1.47 to 2.16. Predictors of contravention of the highway code (the first two predictors) were found to be strongly associated with negative attitudes towards "enforcement" and "speed limitations" with an adjusted odds ratio ranging from 1.31 to 2.02. CONCLUSION: Our study supports the view that individuals with a high propensity for driving behaviors associated with an increased risk of RTCs were more likely to have negative attitudes towards traffic safety. Changing drivers' negative or distorted opinions of traffic "enforcement" as well as "speed limitations" and "alcohol prohibition on roads" could improve their compliance with road traffic rules.

Awareness of driving while sleepy and road traffic accidents: prospective study in GAZEL cohort.

OBJECTIVES: To examine the association between self assessed driving while sleepy and the risk of serious road traffic accidents (RTAs). DESIGN: Prospective cohort study. SETTING: France. PARTICIPANTS: 13 299 of the 19 894 living members of the GAZEL cohort, workers and recent retirees of a French national utility company followed up since 1989. MAIN OUTCOME MEASURES: Frequency of driving while sleepy in the previous 12 months, reported in 2001; rate ratios for serious RTAs in 2001-3, estimated by using generalised linear Poisson regression models with time dependent covariates. RESULTS: The risk of serious RTAs increased proportionally with the frequency of self reported driving while sleepy. After adjustment for sociodemographic characteristics, driving behaviour variables, work conditions, retirement, medical conditions and treatments, depressive symptoms, and sleep disorders, the adjusted rate ratios of serious RTAs for participants who reported driving while sleepy in the previous 12 months "a few times" or "once a month or more often" were 1.5 (95% confidence interval 1.2 to 2.0) and 2.9 (1.3 to 6.3) respectively compared with those who reported not driving while sleepy over the same period. These associations were not explained by any reported sleep disorders. CONCLUSIONS: Self assessed driving while sleepy was a powerful predictor of serious RTAs, suggesting that drivers' awareness of their sleepiness while driving is not sufficient to prevent them from having RTAs. Messages on prevention should therefore focus on convincing sleepy drivers to stop driving and sleep before resuming their journey.