Climate Change
Global Warming
Air Pollution
Weather & Climate

Climate Change & Sustainable Transport


An effective transport system is vital for economic well-being and good quality of life. There is widespread concern that the continuing growth of transport, particularly road and air transport is damaging to the environment and human health (through vehicle emissions), and to the efficient functioning of the economy (through road congestion). The continued annual ritual of new road building is now considered by the Government to be unsustainable. A sustainable transport policy will require a thorough integration of all modes of transport and land use policies.

Motor Vehicles and their Contribution to Climate Change

In 1998, the transport sector contributed over a quarter of the UK's total carbon dioxide emissions; almost all of this came from road transport. Globally, it is believed that motor vehicles contribute between 14 to 17% of the world's total carbon dioxide emissions. This figure is likely to increase in the coming years.

Motor cars have also been indirectly responsible for emissions of CFCs, used in air conditioning units. Although the "Montreal Protocol on Substances that Deplete the (stratospheric) Ozone Layer" has largely phased out the use of CFCs in the developed world, HCFCs and HFCs are now used widely as replacements. Whilst these gases don't destroy the ozone layer, they are very strong greenhouse gases. It is hoped that these gases, too, will gradually be phased out during the first part of the 21st century.

Emissions of carbon monoxide from motor vehicles may also contribute indirectly to the enhancement of the natural greenhouse effect. Carbon monoxide, although not itself a greenhouse gas, reacts with hydroxyl (OH) radicals in the lower atmosphere. Hydroxyl radicals are usually involved in reactions with methane, another greenhouse gas. If more hydroxyl radicals are removed from the atmosphere by carbon monoxide, more methane will remain in the atmosphere, thereby enhancing the Earth's natural greenhouse effect, by trapping more infra-red radiation. Motor vehicles also emit significant quantities of hydrocarbons and nitrogen oxides. When these gases are exposed to sunlight a photochemical reaction occurs which results in the formation of tropospheric (lower atmosphere) ozone and photochemical smog. Tropospheric ozone is also a greenhouse gas.

If the present rise in global population is accompanied by economic growth and increased personal income, the total amount of motor vehicles could be set to rise beyond 1 billion by 2025, discharging as much as 1,800 million tonnes of carbon into the atmosphere per annum. This would be the equivalent of almost one-third of the 6,000 million tonnes of carbon emissions from all sources today. Without a major improvement in fuel efficiency, a considerable increase in fuel consumption, and consequently greenhouse emissions, will occur.

Reducing Emissions from Motor Vehicles

An attempt to reduce motor vehicle emissions in Europe and the UK by approximately 75% has been made by the introduction of strict new European Community standards, for all new cars produced in the European Community from January 1993. The new legislation enforces the fitting of catalytic converters to all new petrol-engine cars. It is believed that catalytic converters can reduce certain car emissions by 90% or more.

A catalytic converter is a unit about the size of a small shoe-box which fits into the exhaust system of a car. Inside the converter is a honeycomb of ceramic or metal which is chemically treated and coated with small amounts of the precious metals platinum, palladium and rhodium. These convert carbon monoxide, hydrocarbons and oxides of nitrogen into carbon dioxide, water and nitrogen. The principal gas produced is carbon dioxide which, although a greenhouse gas, is less potent then other gases at absorbing infra-red radiation and enhancing the natural greenhouse effect. Controlling emissions of carbon dioxide from motor vehicles will require the use of mandatory fuel efficiency standards.

Catalytic Converter

Sustainable Transport in the UK

In the Sustainable Development Strategy for the UK the Government has acknowledged that it will need to take action to control the rate of traffic growth, improve the environmental performance of vehicles and increase public awareness about the environmental impacts of pollutant emissions from transport. The best approach to promoting a more balanced transport policy will be an integrated approach with both "carrot" and "stick" measures to get people out of their cars. If people are to reduce their dependence on the car, they must be provided with alternatives that are affordable. There are a whole range of measures available to cut carbon dioxide emissions from road transport.

Reducing the need to travel

Emphasis needs to be placed on reversing the trend of population dispersal outwards from urban areas. By effective land-use planning, activities (including work, shopping and leisure) are brought closer together, reducing journey distances to a level where travel on foot and by bicycle becomes more popular. To facilitate this, urban centres need to be made more attractive, and the quality of urban living needs to be improved.

Car pooling

"Car-pooling" is the term used to describe regular journey sharing between a group of drivers, usually to and from work.

Reducing road space

Experience suggests that traffic tends to expand to fill available road space. This process also works in reverse. As road space is reduced, traffic shrinks so the overall level of service is roughly unchanged. This process is termed "traffic evaporation". One of the most effective ways of avoiding traffic growth is simply not to provide for it. Further transfer from car to public transport can occur if the latter is allowed access to large areas denied to car traffic. Pedestrianisation also increases the retail turnover of town centres, contrary to popular belief.

Charging for road space

This provides a way of charging motorists some of the social and environmental costs of car use not reflected in petrol or maintenance costs. Charges can be varied according to peak usage. Unfortunately, the requirement for government legislation for road pricing creates a significant barrier to introducing such a scheme. It is possible that such legislation may be made available to local authorities in the next few years.

Improving public transport

A shift to non-car-based travel will only occur when the quality of public transport service is improved. This will largely include rail, light rail (tram) and bus services.

Cycling and walking

The provision of cycle and pedestrian routes, segregated from road networks, may encourage an increase in the number of short journeys being made by bike or foot. This could be assisted by improving cycle parking facilities at convenient locations, and improving pedestrian access to and within public transport facilities.

Promoting more efficient motoring

Fuel efficiency varies with speed. Above 50mph, fuel consumption increases rapidly. By maintaining slower speeds, fuel is conserved and less carbon dioxide is emitted. In addition, cars driven economically (with reduced acceleration, braking and cornering speed) can save 10% of car fuel.


Motor vehicles generate more air pollution than any other single human activity. Road transport affects local air quality, influences the global climate and creates economic inefficiency through daily road congestion. In the UK, it has been recognised that the continued mismanagement of an unsustainable transport system cannot continue in the future. Sustainable transport policies will involve more than traffic reduction. New technology is required to increase vehicle efficiency and reduce pollution from the traffic that remains. Investment in other modes of transport, including public transport, cycling and walking will be needed to encourage individuals out of their cars.