Jean-Paul Rodrigue (2013), New York:
Routledge, 416 pages.
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:
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
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:
- 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.
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
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:
- 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
- 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).
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
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:
- 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
- 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.
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.
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
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.
- 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.
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.
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.
- 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.