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Transport and sustainability
Transport and sustainability

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2 Transport's environmental impacts

The analysis in the previous section shows that transport energy strategies need to take into account economic, political and social sustainability, as well as being environmentally sustainable. But transport's environmental impacts are proving to be particularly difficult to address.

Transport can produce both direct and indirect environmental impacts (Potter and Bailey, 2008). These are defined as follows.

  • Direct impacts: the results of transport operations, such as pollutants emitted by vehicles, noise intrusion, traffic accident casualties, and the land take of roads, railways and airports (i.e. the amount of land they use).
  • Indirect impacts: how changes in travel behaviour lead to urban sprawl, changes in activity patterns and unhealthy lifestyles.

For transport, the energy impacts tend to be more the direct impacts concerning the source and amount of energy used in vehicles. Existing forms of transport have a high dependency on oil, and are a major source of local air pollution and carbon emissions.

Local air pollution

Local air pollutants from burning transport fuels include:

  • Carbon monoxide (CO) – this is a highly toxic gas that can impair brain function and, in sufficient concentrations, kill. Transport is the major source of CO, with some 90% coming from cars.
  • Nitrogen oxides (NOx) – these cause respiratory problems and contribute to low-level ozone formation and acid rain. Dinitrogen oxide (N2O) contributes to global warming. Transport produces about half of all NOx emissions. Diesel vehicles are an important source.
  • Particulate matter (PM) – this is responsible for respiratory problems and is thought to be a carcinogen. Small particulate matter, known as PM10 and PM2.5 (particles smaller than 10 μm and 2.5 μm in diameter respectively), is particularly dangerous as it can penetrate deep into the lungs.
  • Sulfur dioxide (SO2) – this is an acidic gas that can affect health and damage vegetation.
  • Volatile organic compounds (VOCs) – benzene and 1,3-butadiene are both carcinogens and are easily inhaled owing to their volatile nature. Other chemicals in this category are responsible for the production of ground-level ozone, which is toxic in low concentrations.

To date, the main response to transport's air-quality issues has been the use of technical measures to cut engine emissions (driven by national and regional regulation) coupled with cleaner fuel formulations (a result of international standards). These different aspects will be considered later in this free course.

During the 1980s and 1990s, this approach worked well in developed countries. For example, the UK Air Quality Pollutant Inventory Report (National Atmospheric Emissions Inventory, 2011) stated that 'overall air quality in the UK is currently estimated to be better than at any time since the industrial revolution' (p. 1). Tighter European vehicle emission standards in road transport were largely responsible for a 60% cut in NOx over the same period, and UK emissions of PM10 hydrocarbons declined by 58%. Yet despite such improvements, NOx and particulate emissions remain a source of serious concern, with levels in many UK cities short of acceptable health standards. Some 60% of UK local authorities now have Air Quality Management Areas in an attempt to address this issue. In the USA, despite California's stringent emission standards for cars, air quality for the 14 million inhabitants of the Los Angeles basin currently fails to meet federal standards on around 130 days each year (though this is an improvement on the 226 days on which it failed back in 1988).

In emerging economies, where emission standards are less developed, air pollution remains very severe. In Mexico City the summer smog can be so bad that industrial plants are ordered to cut production and schoolchildren are given the month off. For the 2008 Olympics, Beijing famously banned almost half the city's cars for the duration of the games. In China as a whole, air pollution is estimated to cause around 750 000 deaths annually, making this a very politically sensitive subject (McGregor, 2007).

Transport's carbon dioxide

Even were local air-quality emissions from transport to be successfully addressed, there is a second major issue: the emission of carbon dioxide (CO2) from fossil fuels, and the contribution of this and other 'greenhouse' gases to climate change.

Despite a number of international agreements and actions, CO2 emissions from transport have continued to rise in all countries. This issue was highlighted in the 2006 UK Stern Report (Stern, 2006), where it was noted that between the base measurement year of 1990 and 2002, transport was the fastest growing source of carbon emissions in the rich and developed group of Organisation for Economic Co-operation and Development (OECD) countries (25% growth), and the second fastest growing sector in non-OECD countries (36% growth). Trends indicate that rather than declining over the next 40 years, transport CO2 emissions will grow – particularly in non-OECD countries, whose share of global emissions is anticipated to increase from one third to one half by 2030.

In the UK, the recession in 2009 prevented the quantity of transport emissions in that year from rising compared to 1990. However, with other sectors having cut CO2 emissions, the proportion of emissions coming from transport rose from 15.6% in 1990 to 21.7% in 2009. This share is similar in other EU countries. Over 90% of the UK's transport CO2 emissions come from road transport (Table 2). Passenger cars remain the biggest source of CO2, but road freight emissions are significant and those from light vans have risen substantially. Rail produces only 1.7% of transport's CO2 emissions, despite recent substantial rises in passenger-kilometres and freight carried.

Table 2 UK CO2 emissions by source, 1990 and 2009
SourceEmissions /Mt CO2
Domestic civil aviation1.42.0
Passenger cars73.170.9
Light duty vehicles (vans)9.415.3
Mopeds and motorcycles0.60.6
LPG emissions (all vehicles)0.00.3
Other (road vehicle engines)0.30.1
Domestic shipping1.81.5
Military aircraft and naval shipping5.32.5
Other transport0.30.5
Transport total122.1122.2
Total UK CO2 emissions781.6563.6
Transport as percentage of total CO215.6%21.7%
Source: Department of Energy & Climate Change (2011)

CO2 emissions from aviation have also grown by 40%. Domestic aviation remains a small contributor, but these figures (in accordance with international accounting methods) exclude international aviation. If international aviation is included then aviation accounts for nearly a quarter of all transport's CO2 emissions. The 2004 Transport Policy White Paper (Department for Transport, 2004) noted that because emissions at altitude have a greater global warming effect, these now represent 11% of the UK's total climate change impact.

However, although it was important to first consider CO2 emissions from all types of transport, the focus in this free course will be on surface transport. There is a particular emphasis on travel by car, which – as mentioned above – accounts for a very large proportion of CO2 emissions.