The Environmental Impacts of Transportation

Author: Dr. Jean-Paul Rodrigue

1. The Issue of Transport and the Environment

The issue of transportation and the environment is paradoxical in nature since transportation conveys substantial socioeconomic benefits, but at the same time transportation is impacting environmental systems. From one side, transportation activities support increasing mobility demands for passengers and freight, while on the other, transport activities are associated with growing levels of environmental externalities. This has reached a point where transportation is a dominant source of emission of most pollutants and their multiple impacts on the environment. These impacts fall within three categories:

Direct impacts. The immediate consequence of transport activities on the environment where the cause and effect relationship is generally clear and well understood.
Indirect impacts. The secondary (or tertiary) effects of transport activities on environmental systems. They are often of higher consequence than direct impacts, but the involved relationships are often misunderstood and difficult to establish.
Cumulative impacts. The additive, multiplicative or synergetic consequences of transport activities. They take into account of the varied effects of direct and indirect impacts on an ecosystem, which are often unpredicted.

The complexities of the problems have led to much controversy in environmental policy and in the role of transportation. The transportation sector is often subsidized by the public sector, especially through the construction and maintenance of road infrastructure which tend to be free of access. Sometimes, public stakes in transport modes, terminals and infrastructure can be at odd with environmental issues. If the owner and the regulator are the same (different branches of the government), then there is a risk that regulations will not be effectively complied to. It can also lead to another extreme where compliance would lead to inefficient transport systems with subsidized costs.

Total costs incurred by transportation activities, notably environmental damage, are generally not fully assumed by the users. The lack of consideration of the real costs of transportation could explain several environmental problems. Yet, a complex hierarchy of costs is involved, ranging from internal (mostly operations), compliance (abiding to regulations), contingent (risk of an event such as a spill) to external (assumed by the society). For instance, external costs account on average for more than 30% of the estimated automobile costs. If environmental costs are not included in this appraisal, the usage of the car is consequently subsidized by the society and costs accumulate as environmental pollution. This requires due consideration as the number of vehicles, especially automobiles, is steadily increasing.

2. The Transport - Environment Link

The relationships between transport and the environment are multidimensional. Some aspects are unknown and some new findings may lead to drastic changes in environmental policies, as it did in regards of acid rain and chlorofluorocarbons in the 1970s and 1980s. The 1990s were characterized by a realization of global environmental issues, epitomized by the growing concerns between anthropogenic effect and climate change. Transportation also became an important dimension of the concept of sustainability, which is expected to become the prime focus of transport activities in the coming decades, ranging from vehicle emissions to green supply chain management practices. These impending developments require a deep understanding of the reciprocal influence between the physical environment and transport infrastructures and yet this understanding is often lacking. The main factors considered in the physical environment are geographical location, topography, geological structure, climate, hydrology, soil, natural vegetation and animal life.

The main environmental dimensions of transportation are related to the causes, the activities, the outputs and the results of transport systems. Establishing linkages between environmental dimensions is a difficult undertaking. For instance, to what extent carbon monoxide emissions are linked to land use patterns? Furthermore, transportation is imbedded in environmental cycles, notably over the carbon cycle. The relationships between transport and the environment are also complicated by two observations:

First, transport activities contribute among other anthropogenic and natural causes, directly, indirectly and cumulatively to environmental problems. In some cases, they may be a dominant factor, while in others their role is marginal and difficult to establish.
Second, transport activities contribute at different geographical scales to environmental problems, ranging from local (noise and CO emissions) to global (climate change), not forgetting continental / national / regional problems (smog and acid rain).

Establishing environmental policies for transportation thus have to take account of the level of contribution and the geographical scale, otherwise some policies may just move the problems elsewhere and have unintended consequences. A noted example are local / regional policies that have forced the construction of higher chimneys for coal burning facilities (power plants) and induced the continental diffusion of acid rain. Thus, even if an administrative division (municipality, county, state/province) have adequate environmental enforcement policies, the geographical scale of pollutants diffusion (notably air pollutants) obviously goes beyond established jurisdictions.

In addition to the environmental impacts of the network, traffic and modes, economic / industrial processes sustaining the transport system must be considered. These include the production of fuels, vehicles and construction materials, some of which are very energy intensive (e.g. aluminum), and the disposal of vehicles, parts and the provision of infrastructure. They all have a life cycle timing their production, utilization and disposal. Thus, the evaluation of the transport-environment link without the consideration of cycles in the environment and in the product life alike is likely to convey a limited overview of the situation and may even lead to incorrect appraisal and policies.

3. Environmental Dimensions

Transportation activities support increasing mobility demands for passengers and freight, notably in urban areas. But transport activities have resulted in growing levels of motorization and congestion. As a result, the transportation sector is becoming increasingly linked to environmental problems. The most important impacts of transport on the environment relate to climate change, air quality, noise, water quality, soil quality, biodiversity and land take:

Climate change. The activities of the transport industry release several million tons of gases each year into the atmosphere. These include lead (Pb), carbon monoxide (CO), carbon dioxide (CO2; not a pollutant), methane (CH4), nitrogen oxides (NOx), nitrous oxide (N2O), chlorofluorocarbons (CFCs), perfluorocarbons (PFCs), silicon tetraflouride (SF6), benzene and volatile components (BTX), heavy metals (zinc, chrome, copper and cadmium) and particulate matters (ash, dust). There is an ongoing debate to what extent these emissions are linked to climate change and the role of anthropogenic factors. Some of these gases, particularly nitrous oxide, also participate in depleting the stratospheric ozone (O3) layer which naturally screens the earth’s surface from ultraviolet radiation. It is also relevant to underline that climate change also has a significant impact on transportation systems, particularly infrastructure.
Air quality. Highway vehicles, marine engines, locomotives and aircraft are the sources of pollution in the form of gas and particulate matters emissions that affects air quality causing damage to human health. Toxic air pollutants are associated with cancer, cardiovascular, respiratory and neurological diseases. Carbon monoxide (CO) when inhale affects bloodstream, reduces the availability of oxygen and can be extremely harmful to public health. An emission of nitrogen dioxide (NO2) from transportation sources reduces lung function, affects the respiratory immune defense system and increases the risk of respiratory problems. The emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx) in the atmosphere form various acidic compounds that when mixed in cloud water creates acid rain. Acid precipitation has detrimental effects on the built environment, reduces agricultural crop yields and causes forest decline. The reduction of natural visibility by smog has a number of adverse impacts on the quality of life and the attractiveness of tourist sites. Particulate emissions in the form of dust emanating from vehicle exhaust as well as from non-exhaust sources such as vehicle and road abrasion have an impact on air quality. The physical and chemical properties of particulates are associated with health risks such as respiratory problems, skin irritations, eyes inflammations, blood clotting and various types of allergies.
Noise. Noise represents the general effect of irregular and chaotic sounds. It is traumatizing for the hearing organ and that may affect the quality of life by its unpleasant and disturbing character. Long term exposure to noise levels above 75dB seriously hampers hearing and affects human physical and psychological wellbeing. Transport noise emanating from the movement of transport vehicles and the operations of ports, airports and railyards affects human health, through an increase in the risk of cardiovascular diseases. Increasing noise levels have a negative impact on the urban environment reflected in falling land values and loss of productive land uses.
Water quality. Transport activities have an impact on hydrological conditions. Fuel, chemical and other hazardous particulates discarded from aircraft, cars, trucks and trains or from port and airport terminal operations, such as de-icing, can contaminate rivers, lakes, wetlands and oceans. Because demand for shipping services is increasing, marine transport emissions represent the most important segment of water quality inventory of the transportation sector. The main effects of marine transport operations on water quality predominantly arise from dredging, waste, ballast waters and oil spills. Dredging is the process of deepening harbor channels by removing sediments from the bed of a body of water. Dredging is essential to create and maintain sufficient water depth for shipping operations and port accessibility. Dredging activities have a two-fold negative impact on the marine environment. They modify the hydrology by creating turbidity that can affect the marine biological diversity. The contaminated sediments and water raised by dredging require spoil disposal sites and decontamination techniques. Waste generated by the operations of vessels at sea or at ports cause serious environmental problems, since they can contain a very high level of bacteria that can be hazardous for public health as well as marine ecosystems when discharged in waters. Besides, various types of garbage containing metals and plastic are not easily biodegradable. They can persist on the sea surface for long periods of time and can be a serious impediment for maritime navigation in inland waterways and at sea and affecting as well berthing operations. Ballast waters are required to control ship’s stability and draught and to modify their center of gravity in relation to cargo carried and the variance in weight distribution. Ballast waters acquired in a region may contain invasive aquatic species that, when discharged in another region may thrive in a new marine environment and disrupt the natural marine ecosystem. There are about 100 non-indigenous species recorded in the Baltic Sea. Invasive species have resulted in major changes in nearshore ecosystems, especially in coastal lagoons and inlets. Major oil spills from oil cargo vessel accidents are one of the most serious problems of pollution from maritime transport activities.
Soil quality. The environmental impact of transportation on soil consists of soil erosion and soil contamination. Coastal transport facilities have significant impacts on soil erosion. Shipping activities are modifying the scale and scope of wave actions leading to serious damage in confined channels such as river banks. The removal of earth’s surface for highway construction or lessening surface grades for port and airport developments have led to important loss of fertile and productive soils. Soil contamination can occur through the use of toxic materials by the transport industry. Fuel and oil spills from motor vehicles are washed on road sides and enter the soil. Chemicals used for the preservation of railroad ties may enter into the soil. Hazardous materials and heavy metals have been found in areas contiguous to railroads, ports and airports.
Biodiversity. Transportation also influences natural vegetation. The need for construction materials and the development of land-based transportation has led to deforestation. Many transport routes have required draining land, thus reducing wetland areas and driving-out water plant species. The need to maintain road and rail right-of-way or to stabilize slope along transport facilities has resulted in restricting growth of certain plants or has produced changes in plants with the introduction of new species different from those which originally grew in the areas. Many animal species are becoming extinct as a result of changes in their natural habitats and reduction of ranges.
Land take. Transportation facilities have an impact on the urban landscape. The development of port and airport infrastructure is significant features of the urban and peri-urban built environment. Social and economic cohesion can be severed when new transport facilities such as elevated train and highway structures cut across an existing urban community. Arteries or transport terminals can define urban borders and produce segregation. Major transport facilities can affect the quality of urban life by creating physical barriers, increasing noise levels, generating odors, reducing urban aesthetic and affecting the built heritage.

4. Environmental Externalities

Externalities are an economic concept that refers to activities of a group that have unintended consequences, positive or negative, on other groups and most importantly that those consequences, particularly if they are negative, are not assumed by those causing them. The impacts are therefore "externalized". A common example of a positive externality concerns technology since it obviously benefits the innovative firm but also the whole economy through various productivity improvements or improved convenience. Negative externalities have a lot of relevance over environmental issues, since many of the negative consequences of pollution are assumed by the whole society.

For the environmental externalities of transportation they include the consideration of physical measures of environmental damage and the evaluation of involved costs for the society. The main fallacy underlined by externalities is that the costs attributed to a few sources (e.g. users of cars) must be burdened by many (users and nonusers alike). Knowing the sources of environmental externalities is a relatively easy undertaking, while the evaluation of damage and other costs has not yet reached comparative standards among governmental and non-governmental agencies. The challenge resides over three issues:

Relationships. The nature and extent of the relationships between transport and the environment has to be considered. This is particularly complex as most environmental relationships tend to be indirect and cumulative.
Quantification. Relationships have to be quantified and also a value to environmental externalities should be appraised. This is almost out of the possibility as only general figures, much subject to debate, can be assessed. The quantification of economic, social and environmental costs is very difficult but possible if some simplifications and generalizations are assumed.
Policy making. The level and extent of corrective actions that can be taken to alleviate and mitigate environmental externalities linked to transportation in a way where those contributing bear the consequences of their activities. In view of the two above points attempts at regulation, particularly if they involve a comprehensive framework, can be hazardous.

The costs of environmental externalities can be considered from economic, social and environmental dimensions. The basic types of transportation externalities attributed to the environment fall within air pollution, water pollution, noise, and hazardous materials. Establishing and quantifying environmental externalities is a complex undertaking. Quantification is only at its preliminary stage and many have used this argument to differ the application of several environmental policies by lobbying governments (e.g. acid rain, CFCs and most importantly, climate change). Additionally, the wider the geographical scale the more complex the environmental problem becomes, mainly due to cross-jurisdictional issues. Recent attempt to reach a consensus about climate change have underlined that multilateral environmental agreements are close to be impossible.

The sources / emitters of pollutants rarely bear the consequences of their impacts. This has several implications. First, when specific sources are concerned, like road transportation, users only take account of the direct costs of modal ownership like a car (vehicle, fuel, insurance, etc.). Ownership is often the only entry and utilization cost for several transportation modes. The society generally assumes the role of providing and maintaining infrastructure and any indirect costs like damage to structures and infrastructure, losses in productivity (agriculture and labor), cleanup, health services and damage to ecosystems. Second, the geographic separation between sources and recipients is often acute. Acid rains and climate change are obvious examples. On a local level, a community may be affected by noise levels well over its own contribution (notably near major highways), while another (suburbs) may be affected in a very marginal way and still significantly contributes to noise elsewhere during commuting.

There is a tendency towards a shift from direct to indirect consequences for environmental externalities, as of total costs involved. For instance, the absolute levels of air pollutants emissions have considerably dropped in developed countries such as the United States. The problem of source reduction by vehicles was addressed because it was a straightforward cause of air pollutants emissions. This has tended to displace problems elsewhere and developed new types of externalities. Thus, the relative share of air pollution impacts is lessening, but not the number of vehicles, investment in infrastructure or noise levels, which have their own externalities. Reductions in the relative importance of one type of externality redirect the focus on other types that were less addressed, but probably as important in the overall impacts of transport over the environment.

Transfers and additions of costs are very common attributes of environmental externalities. Trying to lessen economic costs will either lessen or worsen social and environmental costs, depending on the externality. For instance, keeping salt as the main de-icing agent is a cheaper solution for authorities responsible for road maintenance, but this practice transfers economic benefits into environmental costs (damage to the ecosystem). In the context of limited resources, the distribution of economic, social and environmental costs takes an important role as what type of damage is most acceptable and in what proportions. It is clear from past strategies that several economic costs have been minimized, notably for producers and users, while social and environmental consequences were disregarded. This practice is less applicable since the society is less willing to bear the costs and consequences of externalities for various reasons (public awareness, high health costs, etc.).

5. Assessing Environmental Externalities

Air pollution is the most important source of environmental externalities for transportation. Although the nature of air pollutants is clearly identified, the scale and scope on how they influence the biosphere are subject to much controversy (see Application 1 for a detailed overview of each air pollutant). On the positive side, emissions of the most harmful air pollutants, such as Carbon Monoxide and Volatile Organic Compounds, have declined in spite of a substantial growth in the number of vehicles an indication of growing levels of environmental compliance of vehicles. Carbon Dioxide emissions have increased proportionally with the growth of transportation usage. Air pollution costs are probably the most extensive of all environmental externalities of transportation, mainly because the atmosphere enables a fast and widespread diffusion of pollutants. As all externalities, costs are very difficult to evaluate because several consequences are not understood, the problems could be at another scale or highly correlated with others and/or a value (monetary or other) cannot be effectively attributed. Two major groups of factors are contributing to air pollution, notably in urban areas.

Structural factors are essentially linked to the size and level of consumption of an economy. Factors such and income and education tend to be proportional with emissions.
Behavioral factors are linked to individualism, consumerism and transportation preferences. Because of convenience and its symbolism, the car is systematically the preferred mode of transportation, even when other modes are available.

From a general perspective, the costs of air pollution associated with transportation can be grouped within economic, social and environmental costs. Externalities related to water pollution are almost all indirect consequences. It is thus difficult to evaluate and to appraise the specific contribution of transportation over various environmental issues, which explains that problems tend to be addressed on a modal basis.

Noise (air and infrastructure vibration) is an inherent characteristic of transportation. Basically, noise is an undesirable sound. The acoustic measure of the intensity of noise is expressed in decibel, db, with a scale ranging from 1 db to 120 db. Noise emissions can be represented as point (a vehicle), line (a highway) and surface (ambient noise generated by a set of streets) sources. Noise pollution is very different from the two categories of pollutant previously discussed as it is only present as vibrations. The internal combustion engine involves combustion, moving parts and friction on the surface over which a transport mode moves. The impacts of noise is strictly local, as vibrations are quickly attenuated by the distance and the nature of the landscape (trees, hills, etc.).

A hazardous material is a substance capable of posing an unreasonable risk to health, safety, and property when transported in commerce. Considering the large amounts of freight being shipped through transport systems, hazardous materials have become a concern. Several hazardous materials (hazmat) releases are spectacular events, notably when it involves a supertanker or a train convoy. However, we must consider that maritime transportation only accounts for 0.1% of the total number of hazmat accidents in the United States, although the volume of hazmat released is higher. Other transportation modes are thus important sources of hazmat release in the environment, even if they mostly involve small quantities. Very limited information is available on the nature and consequences of hazmats released during transportation, except for safety regulations. The effects of hazmat release are always punctual, but intense. The nature of the effect is related to the type of accident and the hazmat involved. It can range from a small scale accident where limited quantities of hazmat are spilled, to important accidents requiring prompt intervention and evacuation of population.

Thus, transportation has a wide array of environmental externalities, some of which can be reasonably assessed while others are mostly speculation (often taken as facts by environmentalist groups). Externalities are also occurring at different geographical scales, and some may even overlap over several. The bottom line is that better transport practices, such a fuel efficient vehicles, that reduce environmental externalities are likely to have positive economic, social and environmental consequences. The matter remains about which strategy is the most beneficial as in all environmental matters much subjectivity and often ideology prevails.