JRSM >
Volume 99, Number 8 >
Pp. 402-405
1 Research Fellow
2 Lecturer in Statistics
3 Professor of Epidemiology
4 Senior Lecturer in Sociology, London School of Hygiene & Tropical
Medicine, London WC1E 7HT, UK
Correspondence to: Dr Phil Edwards, Department of Epidemiology & Population Health E-mail: phil.edwards{at}LSHTM.ac.uk
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Design Analysis of road traffic injury death rates per 100 000 children and death rates per 10 million passenger miles travelled.
Setting England and Wales between 1985 and 2003.
Participants Children aged 0-14 years.
Interventions None.
Main outcome measures Death rates per 100 000 children and per 10 million child passenger miles for pedestrians, cyclists and car occupants.
Results Death rates per head of population have declined for child pedestrians, cyclists and car occupants but pedestrian death rates remain higher (0.55 deaths/100 000 children; 95% confidence interval [CI] 0.42 to 0.72 deaths) than those for car occupants (0.34 deaths; 95% CI 0.23 to 0.48 deaths) and cyclists (0.16 deaths; 95% CI 0.09 to 0.27 deaths). Since 1985, the average distance children travelled as a car occupant has increased by 70%; the average distance walked has declined by 19%; and the average distance cycled has declined by 58%. Taking into account distance travelled, there are about 50 times more child cyclist deaths (0.55 deaths/10 million passenger miles; 0.32 to 0.89) and nearly 30 times more child pedestrian deaths (0.27 deaths; 0.20 to 0.35) than there are deaths to child car occupants (0.01 deaths; 0.007 to 0.014). In 2003, children from families without access to a vehicle walked twice the distance walked by children in families with access to two or more vehicles.
Conclusions More needs to be done to reduce the traffic injury death rates for child pedestrians and cyclists. This might encourage more walking and cycling and also has the potential to reduce social class gradients in injury mortality.
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| METHODS |
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Estimates of the average annual number of miles travelled by children aged 0-14 years by mode of transport were obtained from the Department for Transport's National Travel Surveys (a series of household surveys that collect data on personal travel in Britain, based on 7-day personal travel diaries). Travel data were available for the periods 1985-1986, 1989-1991, 1992-1994, 1995-1997, 1998-2000 and 2002-2003. Estimates of annual distances travelled were also provided separately for three indicators of socio-economic status of households: access to vehicles, employment status of head of household, and housing tenure. We used linear interpolation to obtain estimates of the average annual distances travelled by pedestrians, cyclists and car passengers for each year from 1985-2003. These data were then used to estimate death rates/100 000 population and per 10 million passenger miles.
We derived 95% confidence intervals (CI) for the rates using the Poisson distribution. To smooth the fluctuations caused by year-to-year random variation, we calculated 3-year moving averages, except for the start and end of the period, 1985 and 2003, where 2-year averages were calculated. To quantify changes in the mortality rates over time, we calculated the ratio of rates in 2003 to those in 1985. A Poisson regression model was used to derive 95% CI, with year as the independent variable, number of deaths as the dependent variable, and total population or total passenger-miles as the exposure variable. Research ethics approval was not required for this study.
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Figure 1 shows trends in the modes of transport used by children since 1985. By 2003 the average mileage travelled as a car occupant had increased by 70%, the average mileage walked had declined by 19%, and the average mileage cycled had declined by 58%, compared with 1985. Death rates/10 million passenger miles travelled declined over the study period for all modes of transport, although cycling showed the smallest reduction (Table 3). By 2003, for every 10 million miles travelled, there were 0.55 child cyclist deaths (95% CI 0.31 to 0.89 deaths), 0.27 child pedestrian deaths (95% CI 0.20 to 0.35 deaths) and 0.01 child car occupant deaths (95% CI 0.007 to 0.014 deaths). The child pedestrian death rate was 27 times (95% CI 17 to 42) higher than the child car occupant death rate, and the child cyclist death rate was 55 times (95% CI 30 to 100) higher.
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Figure 2 shows the average distances walked annually by children for three indicators of socio-economic status of household. Children from households without access to vehicles, or where the head of household is not working, or where households are rented, all walked further each year than did their counterparts. By 2003, children without access to a vehicle were walking twice the distance walked by children in families with access to two or more vehicles.
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Strengths and weaknesses of this study
It is important to bear in mind that this paper reports an ecologic
analysis. Our inferences about the relative safety of different modes of
travel are based on aggregate data and we cannot assess individual risks from
average distances travelled. There are also acknowledged limitations in both
mortality data and travel survey data for addressing questions of risk
exposure. Using mortality data to estimate injury risks for different modes of
travel avoids the problems of incomplete reporting that can occur with less
severe injury and which may be differential according to mode of travel.
However, there are two problems. First, mortality depends on case fatality and
substantial reductions in injury case fatality have been
documented.6
Although this would explain some of the overall decline in injury mortality
rates, it is unlikely to account for the large differences in risk according
to mode of travel. Second, the observed injury mortality differentials by mode
of travel may not represent the situation for non-fatal injuries. However,
comparisons of risks for those killed and seriously injured and for all
casualties for the whole population suggest the relative risks for the three
modes considered here are
similar.7
For each mode, we calculated death rates per mile travelled, using estimated average annual distances travelled. It is possible that injury risks vary with length of journey. In particular, longer journeys typically taken by car are unlikely to be taken by children as pedestrians or cyclists. However, we were unable to calculate death rates per mile travelled adjusted for journey length, because information about the journey on which deaths occurred is not recorded. An alternative risk exposure indicator is injury rate by hour of journey time. In other studies, comparisons of fatalities per hour and for distance suggest that walking and cycling still have higher risks than car transport, but that the differential is not so great.7
The mortality data used in this study were extracted from ONS data files. During the study period the way that injuries were classified changed as a result of the move from ICD-9 to ICD-10. Although this may have caused discontinuities in the trends that were not due to real changes over time, the results from a comparability study conducted by the World Health Organization suggest that the change to ICD-10 would have had no noticeable effect.8
Non-response in the National Travel Surveys can be as high as 40% and this presents a threat to the validity of the travel estimates. The Department for Transport is currently conducting analyses to assess the impact of non-response on the travel survey estimates but these results are currently unavailable.
We used injury deaths for England and Wales but the National Travel Surveys also include Scotland. There is some evidence that Scottish residents walk and cycle further than the English and Welsh, and so their inclusion may have led to an overestimate in walking mileage.9 However, the effect of overestimating walking mileage would have been to understate the risks per mile walked for pedestrians.
Policy implications
Road danger is a disincentive to active transport. Reducing the traffic
injury risks for child pedestrians and cyclists must be an important part of
any strategy to encourage walking and cycling. Our results suggest that more
needs to be done in this respect. At present, the conditions are set for a
vicious circle of rising road danger leading to more children being driven
which increases traffic volumes adding further to road danger. International
evidence suggests that the number of people walking and cycling is inversely
related to the number of collisions between motor vehicles and pedestrians or
cyclists.3 Thus a
virtuous circle is possible, in which addressing the higher risks of active
transport could encourage more cycling and walking, and thus potentially
further reduce road danger.
Reducing the risks of active transport to encourage more children to walk and cycle has added public health benefits. First, the increased physical activity may help to stem the rising levels of childhood obesity. Second, reductions in the use of motorized vehicles would reduce transport related carbon dioxide emissions which is a major contributor to climate change. Third, because poor children walk more than more affluent children, efforts to improve the safety of walking has the potential to reduce the steep social class gradients in child injury death rates.
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Funding This work was undertaken by the London School of Hygiene & Tropical Medicine who received funding from the Department of Health. The views expressed in the publication are those of the authors and not necessarily those of the Department of Health.
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