Transport and Health in London



a Report for the DEPARTMENT of HEALTH


Stephen Glaister, Dan Graham and Ed Hoskins

Department of Civil Engineering

Imperial College of Science, Technology and Medicine

London, SW7 2BU October 1999



This report reviews the literature on the relationship between transport in London and the health of Londoners and thus its impact on health services in London.

It does not comment on the wider impacts that traffic in London may have in contributing to the greenhouse effect or to acid rain. However in this respect it should be noted that national road traffic is not the main source of these pollutants contributing about 22% of CO2 and only 2% of SO2.

We have set out some firm conclusions in the following paragraphs. However, we recognise that uncertainty surrounds these conclusions. This was commissioned as a limited-scale, initial investigation and there are bound to be important sources that we are not aware of.

There is a fair quantity of data available but it is not easy to deduce unambiguous conclusions from it. There is much variability in the phenomena being observed at the national level and the data is inevitably less decisive in relation to London, which has special characteristics, yet is a vast geographical area.

Further, circumstances in London are changing quickly and this compounds the difficulties of accurate observation. As we report, where careful statistical work has been carried out in various parts of the world it has proved difficult to make estimates with a high degree of confidence. Much work remains to be done to test, reject or confirm the conclusions we set out here.

As far as London is concerned we draw the following conclusions:

  • Public opinion is strongly of the view that traffic congestion and air pollution remain major problems in London and that traffic-generated air pollution damages their health
  • Central government, its agencies and local government actively promote atmospheric pollution as a major health problem in London
  • The level of toxic vehicle emissions is falling both nationally and in London. In London it is falling particularly rapidly, as a result of the introduction of catalytic exhaust gas converters in 1992, particle traps, improved engine technology, improved fuels and tax incentives. These improvements are set to continue in spite of national traffic growth, which is not matched in London itself. Continued efforts to reduce particulate emissions remain worthwhile, and can be achieved by the enforcement of existing legislation. A large proportion of this kind of pollution comes from a small proportion of the vehicles
  • London is now one of the world’s least air-polluted megacities (over 10m inhabitants) according to WHO and UNEP standards. It is in advance of New York and Tokyo and Los Angeles, which has particular geographic and meteorological problems that cause the concentration of atmospheric pollution.
  • Government and its agencies could promote London as an essentially healthy city from the point of view of atmospheric pollution. Smoggy London ceased to exist in the 1950’s and traffic emissions have diminished rapidly in the 1990’s. On the other hand London can not be promoted as a city free of filth, rubbish and litter.
  • The DoH COMEAP discounts the health effects of all but three traffic related pollutants: SO2, particulates and ozone. These outcomes can be summarised as follows: ·
    • Lead emission from traffic has been almost eliminated.
    • Carbon monoxide from traffic (as opposed to smoking) is not a health problem in the concentrations normally encountered in London.
    • Ozone levels are lower in London than in most other parts of the country. · In early to mid 1990’s traffic was responsible for over 20% of the SO2, but measurements in Central London indicate that this had fallen substantially by 1998.
    • Similarly, traffic used to be responsible for over 75% of particulates, but there appears to have been a dramatic fall since 1996. The attributable additional costs to the DoH of these factors in the demand for additional services are small.
  • In 1998 the costs to the NHS directly attributable to traffic in London were of the order of: Accidents £ 94m about 1 50th of the London NHS medical budget Pollution £ 7m about 1 600th of the London NHS medical budget
  • In the international literature, where adverse health effects have been identified the uncertainty around the ‘damage’ or ‘cost’ estimates of emissions is typically large. The high degree of uncertainty is due to an absence of reliable data and the variability of circumstances. Where authors have reported ‘best’ estimates of the external costs associated with road transport emissions these are often small.
  • The efforts now in progress at national and local level to introduce and attain National Air Quality Standards and to put in place Low Emission Zones do not appear to have been given a justification on grounds of saved health costs. They may not be justified on grounds of the avoidance TRANSPORT and HEALTH in LONDON page 5 of the occasional discomfort of air quality incidents.
  • The economic basis of the levels set for National Air Quality Standards should be scrutinised, with reference to the estimated benefits and with full attention to costs of compliance borne by individuals and the local economy. The significance of exceedences of such artificial standards on health is not evident, except in the promotion of adverse publicity
  • The international literature suggests that emission levels and their costs vary quite substantially by vehicle type, fuel type, location of use and age. There is some evidence that targeting specific vehicle types and ages could significantly reduce emissions. The most damaging pollutant from a health point of view is probably particulates – often generated by old design or badly maintained diesel engines – produced in urban areas.
  • Continuing efforts should be made to reduce atmospheric pollution from particulate matter and existing measures should be enforced. This may be justified on the basis of reduced health risk but possibly not on the basis of saved health costs.
  • There may be evidence that particulates, especially PM2.5 , can cause damage to health in the long term. The reductions in particulate emissions now in train are wholly beneficial but they will not necessarily reverse the damage caused in previous decades.
  • Lead can now be disregarded as a health threat and the history of its elimination is an illustration of how a mixture of fiscal incentive and appropriate physical regulation can stimulate rapid change in behaviour. This experience and success in reducing particulates to date both point towards means for achieving more in this area.
  • Better quality diesel fuels have made a contribution in the past and continued attention to the fuels used is warranted – including consideration of fundamental changes to new kinds of fuel.
  • Traffic reduction in London will probably only be justified on the basis of the non-health costs and benefits. Few traffic reduction measures are justifiable on health grounds.
  • For London, congestion charging, if it is implemented by the elected Assembly, is likely to have a more noticeable impact on local traffic volumes than fuel-price based instruments. The further effect on air quality would probably be small and this is also true of other traffic management measures – even though they may be highly beneficial for other reasons.
  • Even though the UK has a good comparative record on traffic accidents, there should be concern that the numbers of some types of accident (cycle and car) in London are currently rising.
  • However worthwhile improvements to the health of individuals would be achieved by the promotion of a modal shift from the use of the car to walking or cycling, especially if this can be achieved without an undue increase in the numbers of road traffic accidents.



Note on the conclusions for Nitrogen Oxides (NO – NO2) NOx

Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. The principal source of nitrogen oxides – nitric oxide (NO) and nitrogen dioxide (NO2), collectively known as NOx – is road traffic, which is responsible for approximately half the emissions in Europe. NO and NO2 concentrations are therefore greatest in urban areas where traffic is heaviest. Other important sources are power stations, heating plants and industrial processes.

Nitrogen oxides are released into the atmosphere mainly in the form of NO, which is then readily oxidised to NO2 by reaction with ozone. Elevated levels of NOx occur in urban environments under stable meteorological conditions, when the airmass is unable to disperse.

Nitrogen dioxide has a variety of environmental and health impacts. It is a respiratory irritant, may exacerbate asthma and possibly increase susceptibility to infections. In the presence of sunlight, it reacts with hydrocarbons to produce photochemical pollutants such as ozone. In addition, nitrogen oxides have a lifetime of approximately 1 day with respect to conversion to nitric acid. This nitric acid is in turn removed from the atmosphere by direct deposition to the ground, or transfer to aqueous droplets (e.g. cloud or rainwater),thereby contributing to acid deposition.

About half the man made (anthropogenic) element of Nitrogen Oxides are generated by road traffic. However at a global level the naturally generated oxides of nitrogen (arising from bacterial action, volcanic eruptions and lightning) far outweigh the amounts generated by man.

Thus NOx at low concentrations could reasonably be regarded alongside CO2 as a natural constituent of the atmosphere. Thus although a contribution to acid rain is made by NOx from road traffic, contributions are also made from other sources. Overall these are absorbed in nature by the normal operation of the Nitrogen Cycle.

COMEAP Conclusions:  In view of these difficulties and doubts about the relationships between exposure to nitrogen Dioxide and effects on health it was decided not to include nitrogen dioxide in the estimates of the effects of pollutants on health.



Full report