Transport policies and health impact assessment for environmental pollution ; air pollution

Transport policies and health impact assessment for environmental pollution; air pollution



Transportation and transport systems are related to health through multiple routes: as a cause of road injuries, through their contribution to air pollution particularly in urban environments, because of connections with climate change, and because of their influence on levels of physical activity.  Efficient motorised transport is integral to modern living, but many people are now over-dependent on motor transport to the detriment to their health.  A particular concern is the lack of physical activity arising from the displacement of active transport by motorised transport.  Efforts to reduce the volume of urban traffic and to promote walking and cycling are likely to have appreciable net benefits to health.


Key definitions and terms

Active transport

Travel modes that involve physical activity, mainly including walking and cycling.

Health impact assessment

A combination of procedures, methods and tools by which a policy, programme or project may be judged as to its potential effects on the health of a population, and the distribution of those effects within the population.

Health impact assessment may be based on quantitative or (less commonly) qualitative methods.  Related terms include quantitative risk assessment (QRA), which implies a formal quantitative process of estimation, and health impact analysis, which indicates a (usually mathematical) framework for analysing the options in terms of costs and health effects.

Particles/ particulate matter (PM)

Particles or particulate matter (PM), are tiny particles of solid or liquid matter suspended in the air.  Those of less than 10 microns diameter are sufficiently small to enter the lower airways and are of concern because of potential health effects.


A triatomic form of oxygen, which at ground-level ozone is an air pollutant with harmful effects on the respiratory systems of humans and animals.


Transport and health


Transport has multiple connections with health.  While the internal combustion engine and the jet engine brought welcome independence and mobility to many, as well as being key factors in
economic development, there is now increasing recognition of the many negative aspects of fossil-fuel-based transportation.

Transport-related emissions of carbon dioxide and other greenhouse gases are rising.  Without a cleaner fuel source, the growth in motorised land vehicles and aviation is incompatible with averting serious climate change. Moreover the energy intensity of land transport correlates with its adverse health effects, which include:

  • road-traffic injuries;
  • physical inactivity (with consequent effects on obesity, chronic disease, especially diabetes, malignancy, and mental well-being);
  • exposure to urban air pollution;
  • adverse impacts on quality of life and noise exposure;
  • environmental degradation;
  • energy-related conflict;
  • health effects consequent to climate change.

There are also major inequities. For the world’s poor people, walking is the main mode of transport, but such populations often experience the most from the harms of energy-intensive transport, e.g. air pollution and road traffic accidents.

Active transport

The World Health Organisation has pointed out the several health benefits of using transport as a means for regular physical activity through walking and cycling – so-called active transport.
The following facts are taken from the WHO website[1]:

  • In developed countries, physical inactivity is the second most important risk factor for ill health after tobacco smoking.
  • More than 30% of car trips in Europe cover distances of <3 km and 50% of <5 km. These distances can be covered by bicycle within 15–20 minutes or by brisk walking within 30–50 minutes, providing the recommended amount of daily physical activity.
  • In the European Union, though many trips are short, most are made by car. This contributes to over 30% of adults being insufficiently active during a typical week, and to a prevalence of obesity that increased by 10-40% between the late 1980s and the late 1990s.

From a public health perspective, therefore, there appears to be substantial advantage in promoting active transport and wider use of public transport.  To achieve this, cities require safe and pleasant environments for walking and cycling, with destinations in easy reach and, for longer journeys, a safe, reliable and attractive public transport service, ideally powered by energy generated from renewable sources. This sort of change is crucial for achieving transport that is sustainable for health and the environment, a concept that is emphasised by relevant European policy frameworks such as the Transport, Health and Environment Pan-European Programme[2] and the Charter on Transport, Environment and Health[3].

Outdoor air pollution

Motor vehicles are one of the main contributors to outdoor air pollution, particularly in urban environments.  There are many constituents of such pollution (particles, nitrogen oxides, ozone, sulphur dioxide, carbon monoxide, lead, volatile organic compounds). The evidence for adverse health effects is strongest for particles, specifically for particles smaller than 10 microns in diameter, often referred to as PM10, and PM2.5 (particles less than 2.5 microns in diameter) which are sufficiently small to enter the lower airways of the respiratory tract.  Such particles may arise from a number of sources, including combustion processes.  A growing concern is with ground level ozone (O3), which is formed by photochemical reactions in the atmosphere.  Its levels tend to rise during hot weather because its formation is catalysed by sunlight and volatile organic compounds (VOCs) which rise during periods of high temperature.  Ozone effects may therefore be greater during heat waves.

Evidence about the adverse health effects of particles and other air pollutants comes from various forms of epidemiological and other studies. 

Two common types are:

- Time-series studies, which examine (usually) day-to-day variation in health events and how it correlates with fluctuation in air pollution levels.  This form of study provides evidence mainly about the short term effects of pollution, with influence on disease exacerbation.

- The semi-ecological cohort study which compares the well-documented health experience of populations exposed to varying levels of air pollution usually measured over a period of years.  This form of study is important in providing evidence about long-term effects of air pollution exposure, including disease induction, but it is much less common than the time-series study.

The evidence from a large number of studies is now very persuasive that outdoor air pollution is harmful to health, and this has prompted a range of forms of control legislation as described in Section 7.  Although the risks to any individual are small, the population attributable burden of air pollution is appreciable because whole populations are exposed.

To date, there is no convincing evidence for any threshold of air pollution below which harmful effects do not occur.  It is therefore reasonable to assume that the lower air pollution the better from a health
perspective.  Nonetheless, air pollution standards and controls have to set levels on pragmatic grounds.  It is impossible to eliminate air pollution, so the goal is to contain it to acceptable levels. 

Health impact of motorised transport in Europe

One of the difficulties is that transport policies are often driven by demand for motor transport, without proper consideration of the full costs and benefits, including to health.  One mechanism for considering health impacts more appropriately is through the mechanism of health impact assessment (see section below).  A health impact study of traffic related air pollution in three European countries (Austria, France and Switzerland) found air pollution to be responsible for 6% of total mortality or more than 40,000 cases per year – about half of which was attributable to motorised traffic.  Transport also accounted for: more than 25,000 new cases of chronic bronchitis (adults); more than 290,000 episodes of bronchitis (children); more than 0·5 million asthma attacks; and more than 16 million person-days of restricted activities (Kunzli, et al, 2000)[4]

Health impact assessment (HIA)


Health impact assessment is the name given to the procedures, methods and tools by which a policy, programme or project may be judged as to its potential effects on population health.  It may be undertaken using quantitative or qualitative/semi-quantitative means.

Quantitative risk assessment

In addition to the overall burden of health effects, it is also concerned with the distribution of the positive and negative effects, and how good consequences for health could be enhanced and the bad avoided or minimised.  The principles and methods of HIA can be used to assess health consequences as part of another impact assessment such as a Strategic Environmental Assessment or Environmental Impact Assessment.

In the UK, the The HIA Gateway publishes guides, examples and best practices on HIA.[5]

A more formal, quantitative form of impact assessment is often referred to as quantitative risk assessment (QRA).  By convention, this is described as having four stages:

  1. Hazard identification
    Based on review of scientific literature, including toxicological studies and epidemiology, as available.
  2. Exposure-response assessment
    Again based on toxicological and/ or epidemiological data, usually entailing extrapolation of exposure-response curve, and giving rise to uncertainties with respect to thresholds/ intercepts; shape of the exposure-response (extrapolation); and the relationship between risk, intensity and duration of exposure.
  3. Exposure assessment
    Direct measurement is often difficult or costly, so this is often based on indirect, semi-quantitative assessment using: type of exposure, duration, intensity etc.  An exposure matrix may be produced that estimates exposure levels for various population groups defined by location, age etc.
  4. Risk characterisation
    This summarises patterns of risk based on information from Steps 2 and 3 above.

QRA draws on all the available evidence, requires little or no new measurement, and generates results which are statistically stable.  But estimates are indirect (both with respect to exposure & health impacts), and typically many assumptions are necessary (e.g. extrapolations across dose ranges, sometimes from one species to another etc).


Key references

  • Woodcock J, Banister D, Edwards P, Prentice AM, Roberts IP. Energy ad transport.  The Lancet, 2007; 370(9592):1078-1088  (doi:10.1016/S0140-6736(07)61254-9)
  • Künzli N, Kaiser R, Medina S, Studnicka M, Chanel O, Filliger P, Herry M, Horak Jr F, Puybonnieux-Texier V, Quénel P, Schneider J, Seethaler R, Vergnaud J-C, Sommer H.  Public-health impact of outdoor and traffic-related air pollution: a European assessment.  The Lancet 2000; 356:795-801 (doi:10.1016/S0140-6736(00)02653-2)[6]
  • Annalee Yassi, Tord Kjellstrom, Theo de Kok and Tee Guidotti (2001) Basic Environmental Health, OUP, Canada.[7]


Useful websites



                                    © Dr Paul Wilkinson 2009, Helen Crabbe and Rebecca Close 2016