Health effects

CARLOS DORA

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TRANSPORTATION is a major public health issue worldwide. The modes of transport people use for everyday life, how long and how often they travel, all have major implications for the health of both individuals and the population.1 Since transport activities impact on health, both negatively and positively, transport policies become a key determinant of the health of urban populations. To realise the health potential from transport interventions, health, therefore, has to be clearly included in the urban transport and land use policy agendas.

In the 19th century, investments in infrastructure works led to major public health gains in urban areas, a direct consequence of improvements with regard to water, sewage and housing. The new challenge in the beginning of the 21st century is to plan and implement land use patterns and transport systems that avoid traffic injuries, air and noise pollution, promote safe physical activity and enhance social inclusion.

It is worth noting that despite vast research on the adverse health impacts of transport, the evidence has not yet been effectively used to mobilize action in support for sustainable transport policies. Current transport policies are a key determinant of the global burden of disease: road traffic accidents cause 1.2 million deaths worldwide and urban air pollution is estimated to cause around 800 thousand deaths in urban areas every year (65% of which are in Asia). Transport is also a root cause of physical inactivity which causes 1.9 million deaths every year, of noise pollution, of climate change and of psycho-social well-being.

There is considerable evidence that transport-related air pollution contributes to short-term and long-term increases in ill-health and mortality including cardiovascular and respiratory diseases, upper and lower respiratory infections, and lung cancer. These health effects can be attributed to a mixture of pollutants. Particles of less than 10 or 2.5 microns in diameter (PM 10 and PM 2.5) are a good indicator of the air pollution mix that people are exposed to, with the smaller particles reaching deeper into the lungs. Particles are emitted by road vehicles and are composed of carbon, heavy metals and carcinogens such as benzene. Increasing concentrations of PM are directly associated with greater health impacts, the effect being stronger for particles of PM 2.5, coming from combustion engines. There is a 3.4% increase in mortality for every 10 microgram/m3 of PM 2.5 and 0.6% increase for PM 10.2 No threshold could be identified below which health effects were not found, even for concentrations as low as 8 micrograms/m3 for PM 2.5 and 15 micrograms/m3 for PM 10. Since small particles can get indoors freely and can travel long distances across national boundaries, neither the indoor environment nor distance from roads offers much protection from PM.

 

A large proportion of air pollution emissions is attributed to transport, especially in urban areas with large volumes of road traffic. The proportion of exposure to air pollution due to transport may be even higher as air pollutants concentrate in the vicinity of (up to 250 meters away from) urban highways, and in street canyons.3 In addition, levels of air pollutants in vehicles (underground trains, cars, and to a lesser extent buses) are a few fold higher than around cyclists or pedestrians on the same street/area.4 Faster breathing rate and longer length of travel by bicycles in some European cities has shown no net difference in exposure to air pollutants between motor vehicle and bicycle users. Journey time exposures contribute disproportionately to the total exposure, as people may spend hours a day commuting.

The health effects of air pollution observed in epidemiological studies seem to be greater in lower socioeconomic groups. One of the reasons for this phenomenon may be cumulative factors increasing chances for personal exposures and/or greater personal susceptibility in lower socioeconomic groups.5

Reduction in air pollution has been quickly followed by reductions in mortality, as observed in Dublin6 and Hong Kong7. These observations are consistent with the time series studies (showing that daily variation in health status of the population follows changes in air pollution) as well as with a study in California indicating improvement in lung function development in children moving to less polluted areas and worsening lung function development among children moving to more polluted areas.8

 

The transport sector is the fastest growing contributor to green house gases (GHG). In 1990 it produced 13% of global GHG emissions and its total contribution is expected to more than double by 2020.9 The IPCC considers transport as a sector where major opportunities exist for reduction of climate change gases, as substitutes and alternatives exist. Equally there is a wide range of co-benefits from transport policies that reduce GHG through the direct impact on air pollutants, injuries and physical activity.

Burning of fossil fuels over the last 50 years have produced large quantities of GHG, thereby affecting the global climate. The global average temperature has increased by around 0.6 degrees centigrade over the last century and is expected to go up by between 1.4 and 5.6 degrees centigrade over this century.10

 

Shifts in rainfall from climate change affect supply of fresh water and increase the risk of water borne diseases; together with higher temperatures this change affects food production, increasing the risks of malnutrition. Vector-borne diseases may affect regions without population immunity in view of changes in the length of transmission and altered geographical range. A clear example is dengue, the most important viral vector borne disease globally. Dengue transmission has increased dramatically, especially in urban areas, in view of rapid unplanned urbanization, expansion in the number of breeding sites for the aedes mosquitoes and high human population density supplying a large number of susceptible individuals.11

City populations are, therefore, specially vulnerable to climate change health impacts even as they are partly responsible for climate change. Incidentally, developing country cities too are increasingly becoming contributors of climate change gases. On the other hand cities can reduce vulnerability to climate change health impacts; they can also lower production of climate change gases through land use and sustainable transport measures that will have a number of co-benefits for public health and quality of life (through traffic injuries, ambient air pollution, noise, severance and congestion abatement). These connections are key to identifying the right policies for sustainable transport and public health.

 

Road traffic injury (RTA) is already the ninth leading cause of death world-wide and is expected to become the third highest cause of death. Pedestrians, cyclists and motorized two and three-wheeler riders are the road users most vulnerable to traffic injury, and have the highest risk of death per km travelled of all transport modes.12 People aged over 60 years have the highest death rates per 100,000 population than other age groups in low and middle income countries.13

The bulk of road users in middle and low income countries will continue to be pedestrians, cyclists, motorised two and three wheeler riders and public transport users. It is essential, therefore, that transport policies give priority to the safety of these user groups in order to promote public health and ensure health equity.14 Unfortunately, policies more often focus on the private car user instead. The World Report on Traffic Injury Prevention reviews effective policies and measures to prevent RTA.

These include: (a) land use and transport policies such as the promotion of high density and mixed use developments where work, residence, and entertainment are all nearby. (b) Policies to reduce the need for motorised transport by providing shorter and safer routes for vulnerable road users; separating motorized and non-motorized traffic and discouraging private cars from entering city centres or encroaching into pedestrian space.15 Encouraging the use of safer modes of travel such as public transport, as well as cycling and walking that pose less risk to others than do motor vehicles, are also effective. In particular, the quality and safety of public transport services needs to be assured. Enforcing speed and alcohol limits are among the most effective preventive measures, as are the enforcement of child restraints, safety belts and helmets among users of two-wheelers.

 

Both developing and developed countries are today facing an epidemic of non-communicable diseases16 and lack of physical activity and obesity are among its main root causes. Cycling and walking for daily activities can bring major health benefits – half an hour a day can halve the risk of developing heart disease, equivalent to the effect of not smoking.17 Even if spread over two of three shorter episodes, this amount of physical activity can halve the risk of developing adult diabetes and of becoming obese, of certain cancers, as well as reduce blood pressure, osteoporosis and improve functional capacity. These improvements can be expected for 60% of the world population who otherwise engage in little physical activity.18

 

A large proportion of trips in urban areas are short. These provide a good opportunity for daily exercise required for health benefits since 15 minutes is the average time needed for a 2 km walk of a 3-5 km cycling trip. However, the enormous potential saving on the health care costs provided by the higher levels of cycling and walking for daily activities in many parts of the world is rarely recognized. On the contrary there is now a trend in many cities in emerging economies to adopt transport policies that discourage cycling and walking. These policies are likely to create a very substantial health burden in the future, and a large bill considering the high costs of treating the range of chronic diseases caused by physical inactivity.

The risks of accidents is an important deterrent to cycling. To obtain and maintain the levels of cycling and walking needed to protect public health, it is essential to guarantee safe cycling and walking. Under road safety conditions such as found in the United Kingdom since the early 1990s, the health benefits from cycling were estimated to be 20-fold greater than the health risks associated with cycling.19

Recent research demonstrates that the built environment has a key role in the promotion of physical activity and on public health. The growing sprawl in the US has been associated with obesity, lack of physical activity and hypertension.20 Interventions to promote cycling have shown not only remarkable savings on health care costs (4.5 million Euros) but also other health benefits including 20% reductions in road traffic injuries, 20% reduction in all cause mortality among 15-49 year olds.21 Infrastructure investment to improve cycling and walking showed positive cost-benefit ratios of 4, 14 and 3 in three different Norwegian cities.22

 

A large share of the risks to health from transport occurs in urban areas. Urban dwellers are particularly exposed to those risks as humans and vehicles share the same restricted space. Half the world population already lives in cities. Over the next thirty years the population of the world’s cities is expected to double to over five billion people, and almost all of this growth will take place in developing countries. Health risks from transport thus constitute a public health problem of the very first order.

Transport policies in cities worldwide are designed with the private car in mind though the vast majority of the world’s population is unlikely to own a car for the foreseeable future. Nevertheless, they will suffer from traffic congestion and the health risks from pollution, traffic accidents and barriers to cycling and walking, while not benefiting from private mobility. The poor tend to suffer most from the risks of transport, as they are the group most likely to cycle and walk for transport; they live and work on the streets, travel longer distances to and from work, and use more hazardous vehicles, such as two wheeler mopeds.23

 

Unhindered motorization shapes cities and communities (urban sprawl), increases travel distances engendering health risks (less physical inactivity, longer exposure to pollutants and risk of injury), in turn triggering more sprawl, motorization and noise. Noise can interfere with mental activities requiring attention, memory and ability to deal with complex analytical problems. Adaptation strategies, such as tuning out and ignoring noise, and the increased effort needed to maintain performance have been associated with high blood pressure and elevated levels of stress hormones. Loud noise not only increases aggressive behaviour in predisposed individuals, levels above 80 dB reduce ‘helping’ behaviour (people’s willingness and availability to help others.24

In addition, the growth in the use of the car has affected social contact through the so-called community severance effect: the divisive effects of a road on those in the locality. Busy streets have been linked to loss of community cohesion and pose limits to social development (Table I).25 Children are especially vulnerable to environment air pollution and injures, and traffic noise can limit their learning ability. High traffic density affects children’s development. Fewer and fewer children are being allowed to walk or cycle even short distances, because parents are worried about accidents. Indeed, several studies point out that the space within which children can move freely shrinks significantly as street traffic increases in the immediate environment. Children have become more dependent and less physically active, while parents have less time to spare. This reduction in levels of physical activity not only has longer-term effects on physical well-being but can also affect children’s stamina, alertness at school and academic performance.

TABLE I

Road Traffic and Networks of Social Support

Traffic levels

Contacts living on the same street

 

Friends

Acquaintances

Light traffic (200

   

vehicles at peak hour)

3.0

6.3

Moderate traffic (550

   

vehicles at peak hour)

1.3

4.1

Heavy traffic (1900 vehicles at peak hour)

0.9

3.1

 

Urban transport policies have overlooked the health and security function provided by street vendors, and pedestrians in general, as streets with people are safer from violence and traffic injuries. Small street businesses provide livelihoods, which contributes to the health of individuals and their families. Street vendors and other workers in traffic, like policemen, suffer more from air pollution disorders and are at higher risk from traffic injuries.

The experience in a number of cities has shown that better transport systems can be developed in relatively short time periods and address a wide range of issues – from congestion to social inclusion of different groups in the population.

Some of the key ingredients are: (a) Transport demand management: city planning that emphasizes proximity between home and work/markets/leisure/study places, thus reducing the need to travel and exposure to transport health risks. (b) Priority to transport modes with least risks to health per unit of travel: low pollution, low injury risk, enhancing physical activity. Priority in the urban space should be allocated to public transport, cycling and walking, with connectivity between these modes assured. (c) Protection of vulnerable road users – pedestrians and cyclists should be assured dedicated space and protection in road design. Public transport and urban space should be accessible to all levels of physical ability.

 

Experience highlights the limitations of narrowly focused interventions in delivering the expected health benefits as several health risks from transport are closely related. For example, the impact of technical solutions to reduce air pollution based purely on technology improvements may be quickly cancelled out by the added growth in motor vehicles and increased travel distances. Though environmental assessments of transport policies often claim to lead to health improvements, these assessments systematically overlook the health benefits of increased physical activity through shifts in transport, even though this is one of the main preventive factors.

By and large the technical answer to transport problems are known by experts, including in developing countries. The more salient question is what to do to place those transport solutions high on the agenda of municipalities and other policy-makers. For example, an analysis of three cities in Africa showed that although experts knew the technical answers to urban transport problems, the cities lacked clear ‘champions’ for transport, and their organizational structure was unable to respond in a coherent and focused manner. The study concluded that what was missing was leadership and coordination, and recommended a reorganization of the way transport is planned and developed in these cities.

However, the drive and support for that reorganization still needs to come from somewhere, and part of the equation relates to how sustainable transport solutions become a priority in a context of competing problems and agendas of a city. The globalization of economic activity is one such driver as it has enhanced the role of the city. In developing countries, cities are production sites not only for manufacturing, but also for global services like call centres or back offices. Quality of life offered by these cities can be an important part of their competitive advantage in the globalized economy, with concerns about risk of traffic injuries, or of levels of air pollution becoming important considerations to attract the right workforce. Although these macro-economic reasons matter for certain cities, for the vast majority local issues are more likely to influence decision-making.

 

What are the questions that can touch the passion and drive the action of policy-makers? Who will benefit? What types of gains will result from adopting specific transport policies? We argue that it is crucial to highlight the impacts of sustainable transport solutions on a range of tangible benefits, and how they directly affect individuals, their families, friends, and the politicians who represent them. Achieving greater clarity is not simply a matter of marketing or communication, but a question of using relevant data to evaluate the performance of transport measures, data that can convey issues of central concern to the city population and interests.

 

The evaluation of performance of transport policies should involve documentation of all the health impacts those policies are expected to have on the cities’ residents and visitor populations. There is abundant scientific evidence on the links between transportation and a wide range of risks to health that allow the rapid development and testing of the health footprint of transport measures. An efficient communication of these results can influence concerned groups, including globalized businesses in search of lower risk and higher quality of life for their workforce. The same results can also help identify health inequalities resulting from transport and the population groups so far excluded from health protection.

Such an assessment of a ‘health footprint’ from transport should provide a focus for the evaluation of gains from sustainable transport that speaks to the hearts and minds of the people who constitute the political make up of a city. These ‘footprint’ assessments should facilitate the benchmarking of a city’s transport performance and become an incentive for cities to adopt and strengthen sustainable transport policies. They should also open the way for communicating more effectively the gains from sustainable transport policies and measures to city stakeholders and citizens, and make those measures more widely understood and desired. What is lacking is a concerted effort to measure the health footprint over a range of real life transport interventions, and to make the results of that initiative widely known. It is high time that we move in this direction.

 

Footnotes:

1 M. Hillman, Cycling Towards Health and Safety. British Medical Association, London, 1992, 111-121.

2. J. Schwartz, et. al., ‘The Concentration-Response Relationship Between PM 2.5 and Daily Deaths’, Environmental Health Perspectives 110(10), 2002, 1025-1029.

3. E. Buringh, et. al., On Health Risks of Ambient PM in the Netherlands. Executive Summary. National Institute for Public Health and the Environment (RIVM), Bilthoven, 2002.

4. E. Sanderson, et. al., ‘Human Exposure to Transport-Related Air Pollution’, in M. Krzyzanowski, B. Kuna-Dibbert and J. Schneider (eds), Health Effects of Transport-Related Air Pollution. World Health Organization Regional Office for Europe, Copenhagen, 2005.

5. M.S. O’Neill, et. al., ‘Health, Wealth and Air Pollution: Advancing Theory and Methods’, Env Health Perspectives 111, 2003, 1861-70.

6. L. Clancy, et. al., ‘Effects of Air Pollution Control on Deaths in Dublin, Ireland: An Intervention Study’, Lancet 360, 2002, 1210-14.

7. A.J. Hedley, et. al., ‘Cardiorespiratory and All-Cause Mortality After Restrictions on Sulfur Content of Fuels in Hong Kong: An Intervention Study’, Lancet 360, 2002, 1646-1652.

8. E.L. Avol, et. al., ‘Respiratory Effects of Relocating to Areas of Differing Air Pollution Levels’, American Journal of Respiratory and Critical Care Medicine 164, 2001, 2067-2072.

9. R.T. Watson (ed), Climate Change 2001: Synthesis Report. Published for the Intergovernmental Panel on Climate Change IPCC, Cambridge University Press, Cambridge, UK, 2001.

10. J.J. McCarthy, et. al. (eds), Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, UK, 2001.

11. D.J. Gubler and M. Meltzer, ‘Impact of Dengue/Dengue Haemorrhagic Fever on the Developing World’, Advanced Virus Research 53, 1999, 35-70.

12. M. Peden, et. al. (eds), The World Report on Road Traffic Injury Prevention. World Health Organization, Geneva, 2004.

13. M. Peden, K. McGee and G. Sharma, The Injury Chart Book: A Graphical Overview of the Global Burden of Injuries. World Health Organization, Geneva, Switzerland, 2002.

14. B. O’Neill and D. Mohan, ‘Reducing Motor Vehicle Crash Deaths and Injuries in Newly Motorising Countries’, BMJ 324, 2002, 1142-1145.

15. D. Mohan and G. Tiwari, ‘Mobility, Environment and Safety in Megacities: Dealing with a Complex Future’, IATSS Research 24, 2000, 39-46.

16. WHO, Preventing Chronic Diseases: A Vital Investment. World Health Organization, Geneva, 2005.

17. L.B. Andersen, P. Schnohr, M. Schroll and H.O. Hein, ‘All-Cause Mortality Associated With Physical Activity During Leisure Time, Work, Sports, and Cycling to Work’, Arch Intern Med 160(11), 2000, 1621-1628.

18. WHO, op. cit., 2005.

19. M. Hillman, op. cit., 1992.

20. R. Ewing, T. Schmid, R. Killingsworth, A. Zlot and S. Raundebush, ‘Relationship Between Urban Sprawl and Physical Activity, Obesity and Morbidity’, American Journal of Health Promotion 18(1), 2003, 47-57.

21. Odense Municipality (Odense Kommune), Evaluering af Odense-Denmark’s Nationale Cykelby [Evaluation of Odense, Denmark’s national cycle city] (in Danish with English summary). Odense Municipality, Odense, 2004.

22. K. Saelensminde, Walking and Cycling Track Networks in Norwegian cities – Cost Benefit Analyses Including Health Effects and External Costs of Road Traffic. TOI report 567 (in Norwegian). Institute of Transport Economics, Oslo, 2002.

23. D. Mohan and G. Tiwari, op. cit., 2000.

24. C. Dora and M. Phillips (eds), Transport Environment and Health. WHO Regional Publications, European series number 89. World Health Organization Regional Office for Europe, Copenhagen, 2000. Available at URL: http://www.euro.who.int/document/e72015.pdf

25. C. Dora and M. Phillips (eds), op. cit., 2000.

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