Overestimated crash risks of young and elderly drivers.

BACKGROUND: Young and elderly drivers are reported to have markedly greater crash rates than drivers of other ages, but they travel less frequently and represent a minority of road users. Consequently, many crashes involving young or elderly drivers also involve drivers of middle age ranges who travel more frequently. PURPOSE: To examine crash rates of young and elderly drivers, controlling for ages of all drivers involved in collisions. METHODS: A retrospective longitudinal study conducted on population-wide two-vehicle crashes reported in Great Britain from 2002 through 2010 for driver age ranges (17-20, 21-29, 30-39, 40-49, 50-59, 60-69, ≥70 years) and individual driver ages among those aged 17-20 years. Annual trips made, recorded as part of a National Travel Survey, were used to estimate trip-based driver crash rates. RESULTS: Crash rates of drivers aged 17-20 years were not significantly different from crash rates of drivers aged 21-29 years (rate ratio=1.14; 95% CI=0.96, 1.33) when controlling for ages of both drivers involved in two-car collisions, and drivers aged 17 years had the lowest crash rate among drivers aged 17-20 years. Crash rates of drivers aged ≥70 years equaled crash rates of drivers aged 60-69 years (rate ratio=1.00; 95% CI=0.77, 1.32) and were 1.40 times (95% CI=1.10, 1.78) lower than crash rates of drivers aged 50-59 years. CONCLUSIONS: The current findings are in contrast with reports of high crash risks among young and elderly drivers, and suggest that previous reports may have overestimated the crash risks of these drivers by failing to control for ages of all drivers involved in collisions.

Risks of high-powered motorcycles among younger adults.

OBJECTIVES: We assessed whether policies designed to safeguard young motorcyclists would be effective given shifts in ownership toward high-powered motorcycles. METHODS: We investigated population-wide motor vehicle driver and motorcyclist casualties (excluding passengers) recorded in Britain between 2002 and 2009. To adjust for exposure and measure individual risk, we used the estimated number of trips of motorcyclists and drivers, which had been collected as part of a national travel survey. RESULTS: Motorcyclists were 76 times more likely to be killed than were drivers for every trip. Older motorcyclist age-strongly linked to experience, skill set, and riding behavior-did not abate the risks of high-powered motorcycles. Older motorcyclists made more trips on high-powered motorcycles. CONCLUSIONS: Tighter engine size restrictions would help reduce the use of high-powered motorcycles. Policymakers should introduce health warnings on the risks of high-powered motorcycles and the benefits of safety equipment.

Risk of fatal injury in older adult drivers, passengers, and pedestrians.

OBJECTIVES: To compare risk of fatal injury in elderly road users (drivers, passengers, pedestrians) with that of younger age groups and to assess the contribution of elderly road users to the number of reported fatalities in the population. DESIGN: Fatality age was categorized as 21 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, or 70 and older, and road user was categorized as driver, passenger, or pedestrian. Estimated number of trips made by each age group was used to adjust for exposure and to measure individual risk. SETTING: Fatalities recorded in Britain between 1989 and 2009. PARTICIPANTS: Population-wide fatal injury counts in Britain. MEASUREMENTS: Age of fatally injured drivers, passengers, and pedestrians. Estimated number of trips made per year by drivers, passengers, and pedestrians. RESULTS: Risk of fatal injury, but not fatality numbers in the population, were higher for older adult (≥ 70) drivers than for younger age groups. Risk of fatal injury was also high for older adult passengers and pedestrians, who represented the majority of older adult fatalities. CONCLUSION: Previous emphasis on driver impairment in older age has unduly focussed attention on elderly drivers, who represent a minority of all driver fatalities. Older adults represent a much larger proportion of passenger and pedestrian fatalities. Additional policy schemes and initiatives should be targeted at safeguarding older adult passengers and making the road environment safer for elderly pedestrians.

Cycle helmets and road casualties in the UK.

OBJECTIVES: Bicycle helmets have been advocated as a means of reducing injury among cyclists. This assertion, derived from a number of case controlled studies carried out in hospitals, conflicts with results from population level studies. In the Western countries where these case control studies have been performed, it appears that cycling morbidity is dominated by sports and leisure users. The generalizability of studies on helmet effectiveness in relation to utilitarian transport cycling is not clear. This study therefore considers population level data for reported road traffic injuries of cyclists and pedestrians. METHODS: Generalized linear and generalized additive models were used to investigate patterns of pedestrian and cyclist injury in the UK based on the police reported "Stats 19" data. Comparisons have been made with survey data on helmet wearing rates to examine evidence for the effectiveness of cycle helmets on overall reported road casualties. While it must be acknowledged that police casualty reports are prone to under-reporting, particularly of incidents involving lower severity casualties the attractive feature of these data are that by definition they only concern road casualties. RESULTS: There is little evidence in UK from the subset of road collisions recorded by the police corresponding to the overall benefits that have been predicted by the results of a number of published case controlled studies. In particular, no association could be found between differing patterns of helmet wearing rates and casualty rates for adults and children. CONCLUSIONS: There is no evidence that cycle helmets reduce the overall cyclist injury burden at the population level in the UK when data on road casualties is examined. This finding, supported by research elsewhere could simply be due to cycle helmets having little potential to reduce the overall transport-related cycle injury burden. Equally, it could be a manifestation of the "ecological fallacy" where it could be conceived that the existence of various sub-groups of cyclists, with different risk profiles, may need to be accounted for in understanding the difference between predicted and realised casualty patterns.

Epidemiology of child pedestrian casualty rates: can we assume spatial independence?

Child pedestrian injuries are often investigated by means of ecological studies, yet are clearly part of a complex spatial phenomena. Spatial dependence within such ecological analyses have rarely been assessed, yet the validity of basic statistical techniques rely on a number of independence assumptions. Recent work from Canada has highlighted the potential for modelling spatial dependence within data that was aggregated in terms of the number of road casualties who were resident in a given geographical area. Other jurisdictions aggregate data in terms of the number of casualties in the geographical area in which the collision took place. This paper contrasts child pedestrian casualty data from Devon County UK, which has been aggregated by both methods. A simple ecological model, with minimally useful covaraties relating to measures of child deprivation, provides evidence that data aggregated in terms of the casualty's home location cannot be assumed to be spatially independent and that for analysis of these data to be valid there must be some accounting for spatial auto-correlation within the model structure. Conversely, data aggregated in terms of the collision location (as is usual in the UK) was found to be spatially independent. Whilst the spatial model is clearly more complex it provided a superior fit to that seen with either collision aggregated or non-spatial models. Of more importance, the ecological level association between deprivation and casualty rate is much lower once the spatial structure is accounted for, highlighting the importance using appropriately structured models.

Investigating population level trends in head injuries amongst child cyclists in the UK.

Case control studies suggest that cycle helmets offer their wearers protection from injury in the event of an accident. Nevertheless, encouragement and even compulsion of cycle helmet wearing has been controversial. This paper will re-examine another potential source of evidence for the role of cycle helmets. Administrative datasets are attractive because of their availability, but require careful analysis. The results presented here are obtained from analysing such data with an appropriate form of generalised additive model. Whilst helmet wearing surveys in the UK suggest strongly divergent trends in wearing rates between male and female children, there is little evidence from "Hospital Episode Statistics" to indicate similarly divergent trends in terms of head injury. Conversely, it can be confirmed that head injuries are falling faster among cyclists than pedestrians. Although case control studies suggest cycle helmets are not effective in reducing overall injuries, it is worth noting an increase in the proportion of male child cyclists reported by the police as being killed or seriously injured in road collisions. It might be tempting to use these results to suggest that helmets are not effective in reducing head injury at the population level. Whilst the careful analysis of population level data presented here is clearly important, this paper will discuss the reasons why population and individual level analyses of cycle helmets might be different and consider some of the difficulties in assigning cause and effect with imperfect observational data.