4.4 – Transportation, Sustainability and Decarbonization

Author: Dr. Jean-Paul Rodrigue

Sustainable transportation is the capacity to support the mobility needs of a society in a manner that is the least damageable to the environment and does not impair the mobility needs of future generations.

1. Sustainable Development

An issue that has raised concerns relates to the capacity of the global economy to accommodate enduring demographic, economic, and resource consumption growth. Population growth and an increase in living standards allow individuals access to an extensive array of goods and services. Since the 1970s, many statements have been made asserting that the world would be unable to sustain such growth without a possible socioeconomic and environmental breakdown. While these perspectives have been demonstrated to be inaccurate, since resource availability and the quality of life increased, there are concerns that a threshold could be reached at some point, particularly regarding climate change. Under such conditions, sustainable development has been advocated as a priority for future social and economic development.

However, sustainable development is a complex concept that is subject to numerous interpretations since it involves several disciplines and possible interconnections. It is not surprising that the subject is prone to confusion regarding its nature, consequences, and appropriate response. However, it is generally agreed that sustainability favors conditions that benefit the environment, the economy, and the society without compromising the welfare of future generations. Still, as history clearly demonstrates, the conditions of future societies will largely depend upon the legacy of current societies on resources and the environment. All forms of assets (capital, real estate, infrastructures, resources) passed on to the next generation should be at least of equal value (utility) per capita. The basic definition of sustainability has been expanded to include three major pillars (often referred to as the three Es):

  • Social equity. Relates to conditions favoring a distribution of resources among the current generation based upon comparative productivity levels and the promotion of equal opportunities. This implies that individuals or institutions are free to pursue their choice and reaps the rewards for the risk they take and the efforts they make. Social equity is usually the most challenging element of the concept of sustainability to define. It should not be confused with redistribution (or socialism) where a segment of the population agrees or is coerced to support another segment.
  • Economic efficiency. Concerns conditions permitting higher levels of economic efficiency in terms of resource and labor usage. It focuses on capabilities, competitiveness, flexibility in production, and providing goods and services that supply market demand. Under such circumstances, factors of production should be freely allocated, and markets open to trade.
  • Environmental responsibility. It involves a “footprint,” which is lesser than the capacity of the environment to accommodate. This includes the supply of resources (food, water, energy, etc.) and the safe disposal of numerous forms of wastes. Its core tenets include the conservation and reuse of products and resources.

Another important debate relates to what extent public entities (both at the national and supra-national levels) have a role to play. There are competing approaches, one advocating that sustainability be promoted through regulations and the other that the main driver should be market forces and individual behavior. Environmental advocacy groups are dominantly leaning towards regulations. They would argue that sustainability is a much too long-term concept to be addressed by corporations of individuals focused on the short term. A counter-argument could be made that the time horizon of governments, especially democratic regimes, is also very short. In rare instances, governments have shown to be proactive regarding environmental matters. Further, the decision-making and regulatory apparatus of many governments have been captured by special interests, implying that environmental policy is influenced by groups representing contradictory perspectives.

The question remains as if expectations can be placed on entities that seek to optimize positive perception (governments) or on entities that seek to optimize efficiency and profit (corporations and individuals). Paradoxically, while governments tend to be inflexible and unable to adapt, corporations have demonstrated a resounding ability to shift their strategies and provide products that reflect customers’ expectations (including environmentally responsible products). Further, consumer behavior is a key factor in achieving sustainability as it influences the provision and the delivery of goods. It could thus be argued that the private sector is more likely to achieve sustainability than the public sector, particularly since the benefits are apparent. This complex relationship underlines the respective roles of regulations and innovations in achieving a higher level of sustainability.

Societies do not contribute to environmental problems at the same level. Sustainability can be thus expressed at two spatial levels:

  • Global. Long term stability of the earth’s environment and availability of resources to support human activities.
  • Local. Localized forms are often related to urban areas in terms of jobs, housing, and environmental pollution.

Since a growing share of the global population is urbanized, sustainability has increasingly focused on urban areas. Major cities require a vast array of supporting infrastructures, including energy, water, sewers, and transport. A key to urban sustainability issues is linked with the provision and maintenance of a wide range of urban infrastructure. Every city has specific infrastructure and environmental problems. For instance, many cities in developing economies have chronic deficiencies in providing the most basic infrastructure, while their environmental conditions are deteriorating due to congestion and motorization.

Infrastructures can be publicly or privately owned. Public infrastructures have the advantage of being available to a larger share of the population at a low cost (commonly free of access). Still, they are expensive for the government to maintain (subsidies). Private infrastructures tend to service a smaller share of the population, at the choice of the infrastructure provider, but are usually financially profitable. As income levels increase, some infrastructure problems are solved while some environmental problems are created. For instance, an increase in income is linked to better sanitation and water provision, but at the expense of more significant waste generation and carbon dioxide emissions. Global sustainability remains influenced by the paradox of a declining environmental impact per capita of several factors, such as energy consumption and carbon emissions and growth in the net consumption.

2. Sustainable Transportation

Transportation, as a core component supporting the interactions and the development of socio-economic systems, has also been the object of much consideration to what extent it is sustainable.

Sustainable transportation is the capacity to support the mobility needs of a society in a manner that is the least damageable to the environment and does not impair the mobility needs of future generations.

Sustainable development applied to transport systems requires the promotion of linkages between environmental protection, economic efficiency, and social progress. Under the environmental dimension, the objective consists in understanding the reciprocal influences of the physical environment and the practices of the industry and that environmental issues are addressed by all aspects of the transport industry. Under the economic dimension, the objective consists of orienting progress in the sense of economic efficiency. Transport must be cost-effective and capable of adapting to changing demands. Under the social dimension, the objective consists in upgrading standards of living and quality of life.

Automobile dependence is a situation that is often related to an unsustainable urban environment. However, such an observation is at odds with the mobility choice and preferences of the global population, where the automobile is rapidly adopted when income levels reach a certain threshold. Other transport alternatives commonly do not measure up to the convenience of the automobile. Automobile dependency is thus the outcome of market forces expressed as consumer preferences and national manufacturing policies. Private and flexible forms of transportation, such as the automobile, are thus fundamental to urban mobility and should not be discarded as options for the sake of ideological perspectives about what should sustainability implies.

Recent advances in car-sharing technologies and the potential for self-driving vehicles underline a much more sustainable usage of car assets that could remove up to 90% of the vehicles from the streets. This adds up to the ongoing technological improvement in the engine and drive technology, which has reduced vehicle emissions. This contradicts the bias observed in the transport community towards an emphasis on public transit and non-motorized transportation as the dominant, if not sole, strategy towards sustainable transportation. Yet, almost all public transit systems are financially unsustainable, imposing burdens on the society that are accepted because they provide accessibility to all socioeconomic groups. Freight transportation must also be considered in this process, considering the substantial growth of raw materials and goods traded in a global economy. Freight transportation relies much more on environmentally sound modes such as rail and maritime transport.

Measures to promote transport sustainability have their limits. Indeed, the built environment, transport infrastructures, and even modes cannot change quickly enough to solve the bulk of the problems related to unsustainable transport. Most of the investment that is already in place will remain so for 50 years or more. New investments (in additional or improved infrastructure) will not represent much more than a few percentage points changes in reducing traffic congestion and its negative externalities. The different life spans of transport modes and infrastructure underline that sustainability cannot be applied in a synchronized fashion. For instance, it could be possible to replace most of the automobile fleet with more efficient vehicles within a decade. At the same time, road infrastructure (e.g. pavement) would take about a quarter of a century.

While policies, rules, and regulations expect compliance, users tend to instinctively react to price signals and discard modes that are becoming costly (unsustainable) and find loopholes. Transportation and sustainability for both passengers and freight must also contend with mitigation versus adaptation issues:

  • Mitigation concerns the improvement of productivity and efficiency of existing modes, terminals, and managerial approaches so that environmental externalities are reduced. They tend to be short to medium term strategies.
  • Adaptation is a change in the level of use and the market share of respective modes to reflect better a long-term trend, such as higher energy prices, improved information technologies, and stricter environmental regulations.

There is a wide range of environmental sustainability responses, with different local, national, and international regulations. This involves a variety of costs in transport operations that must be built into the price of providing transport facilities and services. Environmental sustainability represents a growing area of responsibility for transport services providers, inciting them to acquire expertise in environmental management. The most important challenge is implementing environmentally sustainable transport within competitive market structures leaning on coping with changes in transport demand while improving transport supply.

3. Managing Transport Demand

To effectively mitigate the adverse impacts of current transportation systems, strategies can be devised to manage (reduce) transport demand for passengers and freight as wells as to redistribute this demand in space or in time (outside peak hours) when possible. Profitable, affordable, and unsubsidized transportation is a good indicator of its sustainability. Increasing transport costs and the pressure to subsidize them can be interpreted as signals that they may be unsustainable. There are several interrelated ways in which transportation systems can adapt to cope with transport demand and reach a better level of sustainability:

  • Full-cost pricing. The full (or partial) recovery of costs related to public investments is incurred in constructing, maintaining, and operating transport networks. They remove artificial signals such as subsidies and let users assume the real transportation cost, including road pricing and pollution (carbon) taxes and fees. Motorists are charged a floating fee (depending on demand variability in peak and off-peak hours) for using targeted roads. This can be implemented through a variety of techniques such as tolls or licensing fees. Tax and pollution fees would involve the implementation of increased taxes on vehicle and fuel purchasing as well as imposing fees on vehicle owners who operate at low levels of energy efficiency. The rationale of such an approach is to provide incentives to influence users towards more sustainable mobility choices.
  • Parking controls. By raising parking prices or reducing the amount of parking space, such a strategy can be used to deter the use of privately-owned vehicles in areas of highest demand by raising the price of commuting by car to high-density areas. The expected result is to encourage (or force) commuters to seek other alternatives either in mass transit, ridesharing, or carpooling. They tend to be ineffective for freight distribution since delivery trucks will infringe regulations for short duration deliveries (e.g. double parking for a few minutes).
  • Trip avoidance. A more direct method of reducing traffic demand, but avoiding trips is a complex endeavor. It involves strategies where an activity still occurs while its related mobility is mitigated. This is mostly related to the use of information technologies, which paradoxically can, at the same time, substitute for and support mobility. For instance, e-commerce can reduce the number of shopping trips, but this involves substituting for parcel deliveries. For freight transportation, trip avoidance is mostly the outcome of changes in sourcing strategies such as nearshoring, where fewer ton-km are generated.
  • Traffic bans. Through traffic bans, the regulatory institution would exert direct control over the allowable limit of vehicles in a given urban area or along specific corridors depending on measures of transport supply-demand functions or arbitrary estimates of carrying capacity. Many high-density central areas have closed streets to pedestrians to create public spaces more conducive to commercial and social activities.

The implementation of such strategies relies heavily on the existing spatial structure, passengers and material flows, and transport networks. An expectation is that the demand will shift towards modes that are more carbon neutral and having a better energy performance. In situations where a fee structure is not effective (e.g. low-income population), constraint-based strategies can be more suitable than fee-based strategies. Such coercive strategies would thereby impose a limit on the number of vehicles in circulation and, correspondingly, reduce congestion and air pollution while promoting alternative transport means. Their fundamental shortfall is they assume that government (planning) entities know solutions to urban transport problems (such as the appropriate number of parking spaces), which is not necessarily the case.

4. Improving Transport Supply

While the implementation of demand-oriented policies and mechanisms are an important component in promoting sustainable transport, these measures can be more effective if coupled with transport supply improvements. Transportation infrastructure should be expanded to accommodate rapidly growing transport demands. As long as the global urban population continues to grow, particularly in developing economies, there are pressures to expand urban transport infrastructures and the infrastructure supporting global trade.

In urban areas, the challenge is to expand and improve transportation supply so that the automobile and trucking can have alternatives. For passengers, this can be achieved by expanding public transit infrastructure, improving existing public transit services, and making cities friendly to pedestrians and non-motorized vehicles. However, it appears that vehicle automation could be an even more effective tool by allowing better utilization of existing vehicle and road assets as well as reducing the number of vehicles in circulation. The realms of green logistics and city logistics have received renewed attention as tools to improve the sustainability of freight distribution since the material needs of economic activities, including end consumers, must be provided for as well.

Sustainability is giving public transit a new impetus since the bulk of its prior rationale was to mitigate automobile dependency and provide mobility to a large share of the population. This is, however, an extremely difficult challenge considering the prominence that the automobile is achieving worldwide. It must be acknowledged that this prominence is the outcome of many positive factors favoring the automobile, such as flexibility, convenience, and relatively low ownership and operating costs. As the average income of the global population is increasing, the pressure for automobile ownership continues. Thus, alternatives can be provided if they prove to be cost-effective while fulfilling a niche demand. They may include:

  • Energy intensity of vehicles and carbon intensity of fuels. Vehicles are the first element of the transport supply, where more sustainable improvements can be implemented. This is the dimension for which the decarbonization of transportation can lead to the most tangible outcomes. There are many strategies, such as using lighter materials (e.g. composites) for manufacturing vehicles or more efficient or new engine technologies. The material intensity of an average vehicle of 1.5 tons remains significant since steel and plastics can account for 75% of its mass. Because of its complexity and related supply chains, the automobile is subject to circular economy considerations where vehicles, parts, and materials could be reused and recycled. Fuels can also be improved upon using alternatives such as natural gas, biofuels, electricity, or hydrogen.
  • Densification and agglomeration. A higher level of concentration of activities usually leads to more efficient transportation uses because of the lesser distances involved. Spatial structures such as logistics zones or transit-oriented developments can thus result in reduced vehicle trips. They may also incite using modes more prone to economies of scale (more passengers or units of cargo per load or surface unit) as cost-effective alternatives. With market signals related to land cost, densification and agglomeration often dictate more efficient and higher density uses.
  • Context appropriate transport. Transportation modes and infrastructure must be developed and used in the context in which they are the most appropriate. However, the relevance of specific transportation systems to service-specific contexts is subject to debate since it is reflective of societal values and priorities. Both public and private forms of transportation have roles to fulfill. The last decades have seen substantial growth of individual mobility despite all the efforts made to promote public transportation. In the North American context, promoting public transit has seen limited success. Therefore, public transportation, being less flexible, should assert a complementary role. The expansion and development of mass transit systems must make effective use of urban space by conforming to a number of factors including urban form, density, and modal preferences. In doing so, the fleets and networks must ensure a level of flexibility while ensuring low ridership costs. Comparatively, methods of improving and upgrading existing public transit services should include improving service coverage and quality and increasing frequency where and when it is most needed (during peak hours). A similar observation applies to freight distribution as a range of modes are available to accommodate a variety of supply chains. There is not necessarily an ideal setting in which a mode should be used.
  • Non-motorized transport modes. The integration of individual modes of non-motorized transport such as walking and cycling can provide access to shopping, schools, and work for a growing share of the population. Also, for cities struggling with serious traffic congestion and air pollution, non-motorized transport should be considered an alternative, or at least complementing, private vehicles while serving as a crucial link in an integrated public transportation system. While cycling can be a challenging mode to promote and integrate into urban transportation (e.g. taxing weather conditions such as winter or excessive heat), there is a clear and unmet need to better integrate pedestrian movements into sound urban design and architecture. For freight, non-motorized transport modes are much more limited in capacity and range.

However, such alternatives contrast with the reality of modal choice towards the automobile and trucks, particularly economies experiencing rapid growth. Thus, sustainable transportation remains elusive since any economic activity, including transportation, has negative environmental impacts. The matter remains if these activities are taking place at a level exceeding the environmental and social carrying capacity. Technological innovation has historically played a paradoxical role of both exacerbating environmental and sustainability issues and, at the same time, offering forms of mitigation. The expectation is that in the future, technological innovation in the transport sector will be more a sustainability driver than it was in the past. This is the main reason why a share of the attention has shifted towards decarbonizing transportation.

5. The Push for Decarbonization

Decarbonizing transportation aims to reduce, mitigate, and even eliminate carbon emissions by adapting transportation infrastructures, conveyances, and operations.

The concept of sustainable transportation has become widely accepted as a goal and appears in the environmental plans of many governments and corporations. Still, sustainable transportation remains elusive as it does not offer clear guidelines, but mostly a narrative allowing stakeholders to remain vague in their commitments and endeavors. For instance, in 2015, the United Nations articulated 17 sustainable development goals covering an outstanding range of issues ranging from reducing economic and gender inequality to eradicating poverty and hunger. Transportation was not identified as a distinct sustainability goal, even if it accounts for about a quarter of global CO2 emissions. Further, these goals have no stated priority and are, therefore, subject to interpretation.

Since the early 2000s, a reframing of sustainability goals in the transportation sector took place towards a more tangible strategy focusing on carbon. This mainly took shape around the decarbonization of transportation, which helps articulate the narrative around fossil fuels. The concept does not undermine the purpose of transportation, which is providing mobility to passengers and freight, but that the carbon footprint of transportation activities should be reduced. Even if it focuses on carbon, decarbonization directly impacts other externalities as most air pollutants are an outcome of the combustion of fossil fuels. Decarbonizing transportation focuses on three main realms of application:

  • Infrastructure. The fixed asset components of decarbonization include transport corridors and terminals. Their construction, maintenance, and upgrade can be subject to procurement strategies that are less carbon-intensive, including the use of materials. Transportation modes, particularly in terms of the economies of scale they offer, can be ranked by their carbon intensity. This implies that infrastructure supporting modes with low carbon intensity should be favored as well as the connectivity (intermodalism) between transportation modes.
  • Conveyances and equipment. For mobile transportation assets, the focus is mainly on their fuel and sources of energy. The electrification of roads and rail is seen as a key strategy as it focuses on modes that have the highest contribution to CO2 emissions. Ideally, urban mobility should have a larger share of accounted by pedestrians and bicycles.
  • Management and operations. A focus is on pricing strategies that change the competitiveness of transportation modes according to their carbon emission. The expectation is that the increasing competitiveness of decarbonized transportation will displace transportation technologies based on fossil fuels. Better utilization of existing transportation assets is also recognized, such as freight platforms and ride-sharing services.

The push towards the decarbonization of transportation mostly concerns electrification and will continue until concerns about climate change have abated. This would imply that the environmental impacts of human activities have been mitigated to a level that is considered to be sustainable. Sustainability and decarbonization are part of the same agenda, with the main difference being that decarbonization offers a clearer framework and plan to action with practical solutions.

Related Topics


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