Author: Dr. Jean-Paul Rodrigue

Transportation activities are significant energy consumers, providing mobility to passengers and freight, which accounts for about 25% of world energy use.

1. Energy

Human activities depend on using several forms and sources of energy to perform work. The more available and affordable energy sources are, the more capabilities and opportunities can be mobilized. The energy content (or energy density) of an energy source is the available energy per unit of weight or volume. Still, the challenge is to extract and use this energy effectively. Thus, the more energy consumed, the greater the amount of work realized, with economic development correlated with higher energy consumption levels. There are four types of physical work related to human activities:

• Modification of the environment. Activities involved in modifying the landscape to make it suitable for human activities, such as clearing land for agriculture, modifying the hydrography (irrigation), constructing infrastructures such as roads, and building and conditioning (temperature and light) enclosed structures.
• Appropriation of resources. Involves the extraction of agricultural resources from the biomass and raw materials (minerals, oil, lumber, etc.) for human needs. It also includes waste disposal, which is, in advanced economies, very work-intensive to dispose of safely (e.g. collection, treatment, and disposal).
• Processing resources. Concerns the modification of products from biomass, raw materials, and goods to manufacture according to economic needs. Since the Industrial Revolution, work related to processing resources was considerably mechanized, initially with simple machines, then assembly lines, and currently with automation.
• Transportation. The mobility of passengers and freight aims to attenuate the spatial inequalities in the location of resources and markets by overcoming distance. The lower the energy costs per ton or passenger-kilometer, the less transportation is an economic burden. Overcoming space in a global economy requires a substantial amount of energy and has consequently been subject to economies of scale. Vehicles and terminal equipment consume energy, while cargo needs to be bundled, sorted, and unbundled.

Lower energy prices in terms of efforts to extract and ease of application involve more opportunities to perform physical work. There are enormous reserves of energy able to meet the future needs of humanity. However, one of the leading contemporary issues is that many of these reserves are not necessarily widely available at competitive costs or are unevenly distributed worldwide. Oil reserves, solar energy, and wind energy are distributed according to well-defined criteria. The geography of energy reveals complex differences in the availability of energy sources and supply and demand patterns. Still, the availability or the competitiveness of an energy source can improve with technological development, implying dynamics in the geography of energy. Even if some energy sources are extracted far from where they are consumed, the massification of transportation enables their mobility, particularly for petroleum and coal.

Throughout the history of energy use, the choice of an energy source depended on several utility factors that involved a transition in energy systems from solid, liquid, and eventually to gas sources. Since the industrial revolution, efforts have been made for work to be performed by machines, which considerably improved industrial productivity. The energy sources used for this mechanization substantially impacted energy demand patterns. The development of the steam engine and the generation and distribution of electric energy over considerable distances have also altered the spatial pattern of manufacturing industries by liberating production from a direct connection to a fixed power system. While in the earlier stages of the industrial revolution, factories located close to sources of energy (a waterfall or a coalfield) or raw materials, mass conveyances, and new energy sources (petroleum and electricity) enabled much greater locational flexibility.

Industrialization placed considerable demands on fossil fuels through its processes and outcomes. At the turn of the 20th century, the invention and commercial development of the internal combustion engine, notably in transport equipment, expanded the mobility of passengers and freight and incited the development of a global trade network. The setting of industrial and energy systems is interrelated. With globalization, transportation accounts for a growing share of the total energy spent on implementing, operating, and maintaining the international range and scope of economic and social activities.

Energy consumption strongly correlates with the level of development, with transportation accounting for between 20 and 25% of consumed energy among developed economies. The benefits conferred by additional mobility, notably in terms of better comparative advantages and resource access, have required a growing amount of energy to support this expanded spatial system. At the beginning of the 21st century, the transition reached a stage where fossil fuels, such as petroleum, dominate. Of the world’s total power production, 80% is derived from fossil fuels, a share that has been steadily declining as an energy transition unfolds.

2. Transportation and Energy Consumption

Transportation and energy can be seen from a cost-benefit perspective, where giving momentum to a mass (passengers, vehicles, cargo, etc.) requires a proportional amount of energy. The matter is how effectively this energy is captured to practical use, which has a strong modal characteristic. The relationship between transport and energy is direct but subject to different interpretations since it concerns different transport modes, each having its utility and level of performance. There is often a compromise between speed and energy consumption related to the desired economic returns. Passengers and high-value goods can be transported by fast but energy-intensive modes since the time component of their mobility tends to have a high value, which conveys the willingness to use more energy. Economies of scale, mainly those achieved by maritime transportation, are linked to low energy consumption per unit of mass transported but at a slower speed. This fits freight transport imperatives relatively well, particularly for bulk, where time is less critical and buffer stock can be accumulated. Comparatively, air freight has high energy consumption levels linked to high-speed services with limited buffer stocks.

The transportation market has a broad spectrum of energy consumption, which is particularly impacted by three issues:

• The price level and volatility of energy sources are dependent on the processes used in fuel production. Stable energy sources are preferred as they enable long-term investments in transportation assets and a constant market supply. Volatile energy prices are not contingent on investments in transport technology.
• Technological and technical changes in the level of energy performance of transport modes and terminals. An important goal is thus to improve this energy performance since it is linked with direct economic benefits for operators (lower operating costs) and users (lower rates). Technological improvements allow access to new motive technologies such as electric vehicles and automation.
• Environmental externalities related to energy use by transport modes, particularly their emissions. Externalities are conducive to regulations related to using specific modes and energy sources and the goal of reducing them.

A trend that emerged since the 1950s concerns the growing share of transportation in the world’s total oil consumption; transportation accounts for approximately 29% of world energy demand and about 61.5% of all the oil used each year. The impacts of transport on energy consumption are diverse, including activities that are necessary for the provision of transport infrastructures and facilities:

• Vehicle manufacture, maintenance, and disposal. The energy spent on manufacturing and recycling vehicles is a direct function of vehicle complexity, the material used, fleet size, and vehicle life cycle. Assembling a ship can take up to two years and requires substantial materials and energy consumption.
• Vehicle operation. Mainly involves energy used to provide momentum to vehicles, namely as fuels, as well as for intermodal operations at terminals. The fuel markets for transportation activities are well-developed.
• Infrastructure construction and maintenance. Building roads, railways, bridges, tunnels, terminals, ports, and airports and providing lighting and signaling equipment require substantial energy. They directly relate to vehicle operations since extensive networks are associated with large amounts of traffic.
• Management of transport operations. The expenses involved in planning, developing, and managing transport infrastructures and operations require time, capital, and skill that must be included in the total energy consumed by the transport sector. This is particularly the case for public transit.
• Energy production and trade. Exploring, extracting, refining, and distributing fuels or generating and transmitting energy also require power sources. The transformation of 100 units of primary energy in the form of crude oil produces only 85 units of energy in the form of gasoline. Any changes in transport energy demand influence the pattern and flows of the world’s energy markets.

Energy consumption has substantial modal variations:

• Land transportation accounts for the vast majority of energy consumption. Road transportation alone consumes, on average, 85% of the total energy used by the transport sector in developed economies. This trend is not uniform within the land transportation sector, as road transportation has been almost the sole mode responsible for additional energy demands over the last 25 years. Despite a falling market share, rail transport, on the basis of 1 kg of oil equivalent, remains four times more efficient for passengers and twice as efficient for freight movement as road transport. Rail transport accounts for 6% of global transport energy demand.
• Maritime transportation accounts for 80% of cross-border world trade, as measured by volume. The nature of water transport and its economies of scale make it the most energy-efficient mode since it uses only 7% of all the energy consumed by transport activities, a figure way below its contribution to the mobility of goods. Still, fuel consumption is an important input in maritime shipping, which is related to ship design (hydrodynamics), utilization level, operational speed, idle time (waiting at ports), and even weather conditions. For terminal operations, figures vary, but a container terminal usually has 70% of its energy consumption provided by fossil fuels (e.g. yard equipment) and 30% by electricity (e.g. portainers).
• Air transportation plays an integral part in the globalization of transportation networks. The aviation industry accounts for 8% of the energy consumed by transportation. Air transport has high energy consumption levels linked to high speeds. Fuel is the second most significant cost for the air transport industry, accounting for 13-20% of total expenses. Technological innovations, such as more efficient engines and better aerodynamics, have continuously improved the energy efficiency of each new generation of aircraft.

Further distinctions in the energy consumption of transport can be made between the mobility of passengers and freight, relying on different modal configurations:

• Passenger transportation accounts for 50 to 60% of the energy consumption derived from transportation activities. The private car is the dominant mode but has a poor energetic performance, although this performance has seen substantial improvements since the 1970s, mainly due to growing fuel efficiency. Only 12 to 30% of the fuel a car uses provides momentum, depending on the type of vehicle. A close relationship exists between rising income, automobile ownership, and vehicle distance traveled. The United States has one of the highest levels of car ownership in the world, with one car for every two people. Another trend has been the increased ownership of minivans, sport utility vehicles, and light-duty trucks for personal use and the corresponding decline in fuel economy. However, fuel consumption is impacted by diminishing returns, implying that higher levels of fuel efficiency involve declining marginal gains in fuel consumption. Also, changes in vehicles-miles traveled are correlated with changes in energy prices, underlining an elasticity for vehicle use. The transition toward electric cars emphasized their disruptive effects on local electric grids, as most vehicles are recharged at home. Urban micro-mobility modes, such as electric bicycles and scooters, also demand additional electric energy on local grids.
• Freight transportation accounts for 40 to 50% of energy consumption derived from transportation activities. Road transportation dominates, accounting for 80% of domestic energy consumption in most economies. Rail and maritime shipping, the two most energy-efficient modes, have more marginal energy consumption levels. Coastal and inland waterways also provide an energy-efficient method of transporting passengers and cargo. Because of these energy advantages, short-sea shipping is considered a transport alternative and part of the transport policies of countries with extensive coastlines. The rationale for favoring coastal and inland navigation is based on lower energy consumption rates and the overall lower externalities of water transportation.

3. Petroleum: The Transport Fuel

Almost all transportation modes depend on variations of the internal combustion engine, with the two most salient technologies being the diesel engine and the gas turbine, since they are the linchpin of globalization. While ship and truck engines are adaptations of the diesel engine, jet engines are an adaptation of the gas turbine. Transportation is almost entirely reliant (90%) upon petroleum products, except for railways using electrical power. While the use of petroleum for other economic sectors, such as industrial and electricity generation, has remained relatively stable, the growth in oil demand is mainly attributed to the growth in transportation demand. Still, the share of oil used in the transportation sector is steadily declining with the introduction of alternative sources such as electric cars. What varies is the type and quality of petroleum-derived fuel being used. While maritime transportation relies on low-quality bunker fuel, air transportation requires Jet-A, a specialized fuel with additives. Road transportation is highly fragmented, with 85% of automobiles depending on gasoline, while 90% of trucks rely on diesel.

The chemical combustion principle of hydrocarbons is worth looking at. For the majority of internal combustion engines, gasoline (C8H18; four strokes Otto-cycle engines) serves as fuel, but other sources like methane (CH4; gas turbines), diesel (mostly trucks), bunker fuel (for ships), and kerosene (turbofans of jet planes) are used. Gasoline produces around 46,000 Btu per kilogram combusted, requiring 16 to 24 kg of air. The energy released by combustion causes a rise in the temperature of combustion products. Several factors and conditions influence the level of combustion in an internal combustion engine to provide momentum and keep efficient operating conditions. The temperature attained depends on the rate of release and dissipation of the energy and the number of combustion products. Air is the most available source of oxygen, but because air also contains vast quantities of nitrogen, nitrogen becomes the principal constituent of combustion products. The combustion rate may be increased by finely dividing the fuel to increase its surface area and, hence its reaction rate and mixing it with the air to provide the necessary amount of oxygen. If combustion were perfect, emissions and thus local environmental impacts of transportation would be negligible, except for carbon dioxide emissions. The challenge is that combustion in internal combustion engines is imperfect and incomplete for two reasons:

• First, the fuel and the oxidizer are not pure, causing imperfect combustion. Although the refining process provides a “clean” fuel, gasoline is known to have impurities such as sulfur (0.1 to 5%) and other hydrocarbons (like benzene and butadiene). In comparison, air is composed of 78% nitrogen and 21% oxygen. Thus, other chemical components are part of the combustion process.
• Second, in part because of the first reason and in part because of the engine technology, incomplete combustion emits other residuals. Combustion in an engine occurs at an average rate of 25 times per second, leaving limited time for a complete combustion process. Besides carbon dioxide and water, a typical internal combustion engine will produce carbon monoxide (CO), hydrocarbons (benzene, formaldehyde, butadiene, and acetaldehyde), volatile organic compounds (VOC), sulfur dioxide (SO2), particulates, and nitrogen oxides (NOx). These combustion products are the primary pollutants emitted into the environment by transportation.

In addition to the imperfect and incomplete combustion of hydrocarbons, three major factors influence the rate of combustion and thus emissions of pollutants, which are the characteristics of the vehicle (where technological improvements can play a role), driving characteristics (where planning and regulation can play a role), and atmospheric conditions. The internal combustion engine converts less than a third of the energy consumed into momentum, primarily due to friction. For electric motors, this figure is above 80%.

4. Transportation and Peak Oil

The extent to which conventional non-renewable fossil fuels will continue to be the primary resource for nearly all transportation fuels is subject to debate. But the gap between demand and supply, once considerable, is narrowing, an effect compounded by the possibility that global oil production will eventually peak. The steady surge in demand from developing economies, particularly China and India, requires additional outputs. This raises concerns about the capacity of major oil producers to meet this rising and enduring global demand. The producers are not running out of oil, but the existing reservoirs may not be capable of producing on a daily basis the increasing volumes of oil that the world requires. Reservoirs do not exist as underground lakes from which oil can easily be extracted. There are geological limits to the output of existing fields. This suggests that additional reserves need to be found to compensate for the declining production of existing fields. Reserves additions may not be enough to offset this growing demand, but technological improvements allowed to tap bitumen and oil shale reserves. However, extracting such reserves necessitates much energy and water. Producing 1 barrel of bitumen requires burning the equivalent of 10-20% of its energy content.

Others argue that the history of the oil industry is marked by cycles of shortages and surpluses. The rising price of oil will render cost-effective oil recovery in difficult areas. Deepwater drilling and extraction from tar sands and oil shale should increase the supply of oil that can be recovered and extracted. Still, there is a limit to the capacity of technological innovation to find and extract more oil around the world, and the related risks can be very high. Adding oil extraction, distribution, and refinery capacity is slow, complex, capital-intensive, and highly regulated. If technically and economically viable, carbon sequestration in CO2 capture and storage could enhance oil recovery from conventional wells and prolong the life of partially depleted oil fields well into the next century.

High fuel prices usually stimulate the development of alternatives, but automotive fuel oil demand is relatively inelastic. Higher prices result in very marginal changes in demand for fuel. The equivalent of $100 per barrel was considered a threshold that would limit demand for automotive fuel and lead to a decline in passenger and freight km. Evidence suggests that higher oil prices had a limited impact on the average annual growth rate of global motorization. The analysis of the evolution of the use of fossil fuels suggests that in a market economy, the introduction of alternative fuels is leading to an increase in the global consumption of both fossil and alternative fuels and not to the substitution of crude oil by alternative fuels. This suggests that in the initial phase of an energy transition cycle, introducing a new energy source complements the existing supply until the new energy source becomes price competitive to be an alternative. The presence of renewable and non-renewable fuels stimulates the energy market with the concomitant increase in greenhouse gas emissions. The production of alternative fuels adds up to the existing fossil fuels and does not replace them.

The main concern is the amount of oil that can be pumped to the surface on a daily basis, especially where major oil fields have reached peak capacity. Under such circumstances, oil prices are bound to rise in the medium to long term, sending significant price signals to the transport market. How the transport system responds and adapts to higher energy prices is subject to much debate and interpretation in terms of the scale and timing of the transition. The following potential consequences can be noted:

• Road. As far as the automobile is concerned, higher oil prices could trigger changes in several phases. Initially, commuters would absorb higher costs by cutting their discretionary spending. Depending on their level of productivity, many economies could show remarkable resilience. The next phase would see changes in commuting patterns (e.g. ridesharing, carpooling), attempts to use public transit, rapid adoption of vehicles with high gasoline efficiency, and a search for other transport alternatives. The existing spatial structure could also show signs of stress as the unsustainability of car-dependent areas become more apparent. There is evidence of an inverse relationship between fuel prices and vehicles -miles traveled in the United States. As high commuting costs and the inflationary effects of high oil prices on the economy become apparent, many would no longer be able to afford to live in a suburban setting. Cities could start to implode. The trucking industry would behave similarly, first by lowering their profits and their operating expenses (e.g. scheduling, achieving full truckload). Still, higher prices will be passed on to their customers eventually.
• Rail. This mode is set to benefit substantially from higher energy prices as it is the most energy-efficient land transportation mode. Rail is about three times more energy-efficient than trucking. The substitution level for passengers and freight remains uncertain and will depend on the current market share and the level of service they offer. In North America, passenger rail has limited potential, while in Europe, and Pacific Asia, passenger rail already assumes a significant market share. North American freight distribution has an advantage for rail freight since rail accounts for a dominant share of tons-km. At the same time, this figure is less significant for other regions of the world, mainly due to the distances involved and the fragmentation of the system. There could be a push toward the electrification of strategic long-distance corridors and the development of more efficient cargo handling facilities. Thus, growing energy prices are likely to affect long-distance rail transportation differently depending on the geographical setting and the conditions of the existing system.
• Air. This mode could be significantly impaired, both for passengers and freight. Air transportation is a highly competitive industry with low profit margins. Fuels account for about 40% of the operating expenses of an air carrier. Still, because most of the other costs are fixed, any variations in energy prices are reflected directly on airfares. A long-term increase in energy prices, reflected in jet fuel, is likely to impact discretionary air travel (mainly tourism), but air freight, due to its high value, can be less impacted. Technological developments are helping to maintain the competitiveness of air transportation with more fuel-efficient planes.
• Maritime. This mode is likely to be relatively unaffected as it is the most energy-efficient, but fuel is an important component of a ship’s operating costs. The response of maritime shippers to higher energy prices tends to be lowering speed (slow steaming), which may impact port call scheduling. In the long run, higher energy prices may indirectly impact maritime transportation by lowering demand for long-distance cargo movements and inciting port calls at ports having the most direct and efficient hinterland connections. In addition, this context may favor the development of short coastal and fluvial services where possible.

Higher energy prices can trigger notable changes in usage, modes, networks, and supply chain management. From a macro perspective, and since transportation is a very complex system, assessing the outcome of higher energy prices remains hazardous. What appears very likely is a strong rationalization, a shift towards more energy-efficient modes, as well as a higher level of integration between modes to create multiplying effects in energy efficiency. As higher transport costs play in, namely for containers, many manufacturing activities will reconsider the locations of production facilities to sites closer to markets (near-sourcing). While cheap and efficient transport systems favored globalization, the new relationships between transport and energy will likely restructure the global structure of production and distribution towards regionalization. This process is also favored by less acute differences in labor costs and a push toward automation.

5. Transportation and Alternative Fuels

The energy source with the lowest cost is usually preferred. The dominance of petroleum-derived fuels results from the relative simplicity with which they can be stored and used in internal combustion engines. Other fossil fuels (natural gas, propane, and methanol) can also be used as transportation fuels but require a more complicated storage system. The main issue concerning the large-scale uses of alternative vehicle fuels is the significant capital investments required in distribution facilities compared with conventional fuels. Another issue is that in terms of energy density, these alternative fuels have lower efficiency than gasoline and thus require a greater volume of onboard storage to cover the equivalent distance as gasoline-propelled vehicles if performance is kept constant.

Alternative fuels in the form of non-crude oil resources are drawing considerable attention due to the non-renewable character of fossil fuels and the need to reduce emissions of harmful pollutants and carbon. The most prevalent alternatives being considered are:

• Biofuels such as ethanol, methanol, and biodiesel can be produced from the fermentation of food crops (sugar cane, corn, cereals; often called first-generation biofuels) or biomass (such as wood and grasses; called second-generation biofuels). Their production, however, requires large harvesting areas that may compete with other types of land use. This limit is related to the capacity of plants to absorb solar energy and transform it through photosynthesis. This low biomass productivity does not meet the energy needs of the transportation sector. Besides, the production of ethanol is an energy-intensive process. Biodiesel can also be obtained from a variety of crops. The choice of biomass fuel will largely depend on the sustainability and energy efficiency of the production process.
• Natural gas is a more efficient and environmentally sustainable fuel for the transportation sector, namely in its compressed form. Although natural gas has been used as a transportation fuel since the early 20th century, its use remained marginal until the late 20th century. It is better fitted for large fleets of vehicles that travel extensively from service points (depots, warehouses), such as public transit buses or delivery trucks. As of 2021, natural gas accounted for 4% of transportation fuel use.
• Hydrogen and ammonia are often mentioned as potential alternatives. The steps in using hydrogen as a transportation fuel consists of producing hydrogen by electrolysis of water or extracting it from hydrocarbons (there are other methods as well). Then, compressing or converting hydrogen into liquid form and storing it onboard a vehicle. Finally, using a fuel cell to generate electricity on demand from the hydrogen to propel a motor vehicle. Hydrogen fuel cells are more energy-efficient than gasoline and generate near-zero pollutants. However, hydrogen suffers from several problems, particularly since much energy can be wasted in production, transfer, and storage. Hydrogen manufacturing requires electricity production. Besides, storing hydrogen requires low-temperature/high-pressure storage tanks, adding weight and volume to a vehicle. This suggests liquid hydrogen fuel would be a better ship and aircraft propulsion alternative. This is where ammonia offers an option as a liquid hydrogen fuel at ambient temperatures that can be easily synthesized with the Haber-Bosch process (invented in the early 20th century) using the nitrogen contained in the air.
• Electricity is being considered an alternative to petroleum fuels as an energy source. A pure battery electric vehicle is considered a more efficient alternative to a vehicle propelled by hydrogen fuel. There is no need to convert energy into electricity since the electricity stored in the battery can directly power the electric motor. Besides, an all-electric car is easier and cheaper to manufacture than a comparable fuel-cell vehicle. The main barriers to the development of electric cars are the lack of storage systems capable of providing driving ranges and speeds similar to those of conventional vehicles. The low energy capacity of batteries makes the electric car less competitive than internal combustion engines using gasoline, but the situation is rapidly evolving to the advantage of electric cars. As of 2022, commercially available electric vehicles had a range of around 550 kilometers (less in real driving conditions), which is steadily increasing with each generation. This is not yet suitable for long-distance travel as their charges are limited, and the charging time can be significant (up to 8 hours for a full charge and 30 minutes for a fast 80% charge), particularly compared with the standard refueling of a gasoline vehicle (5 to 10 minutes). They are better suited for short commuting trips with the residence as the main charging station. As technology improves, the energy and cost-effectiveness of batteries are getting better. For instance, between 2010 and 2020, the cost of lithium-ion batteries fell by 85%. Electric vehicles are eminently suitable for urban transportation for both passenger and freight because of the shorter ranges involved and the availability of recharging stations.
• Hybrid vehicles consisting of a propulsion system using an internal combustion engine supplemented by an electric motor and batteries provide opportunities to combine the efficiency of electricity with the long driving range of an internal combustion engine. A hybrid vehicle still uses liquid fuel as the primary source of energy. Still, the engine provides the power to drive the vehicle or is used to charge the battery via a generator. Alternatively, the propulsion can be provided by the electricity generated by the battery. When the battery is discharged, the engine starts automatically without intervention from the driver. The generator can also be fed by using the braking energy to recharge the battery. Such a propulsion design significantly contributes to overall fuel efficiency, particularly in urban areas where vehicles accelerate and brake frequently. The successful development and commercialization of hybrid vehicles appear as the most sustainable option for conventional gasoline engine-powered vehicles in the medium term.

The diffusion of non-fossil fuels in the transportation sector has serious limitations. While oil prices have increased over time, they have been subject to significant fluctuations. The comparative costs of alternative energy sources to fossil fuels are higher in the transportation sector than in other types of economic activities. This suggests higher competitive advantages for the industrial, household, commercial, electricity, and heat sectors to shift away from oil and to rely on solar, wind, or hydro-power. Transportation fuels based on renewable energy sources might not be competitive with petroleum fuels unless significant energy price increases coupled with substantial technological improvements. A risk concerns the imposition of specific fuels through regulations causing disruptions in capacity and cost. Energy should be a resource available in abundance and effectively managed. If energy becomes scarce, particularly through policy, a whole array of opportunities may be lost, including those related to lower mobility levels.

An emerging trend involves decarbonizing transport intending to make transportation systems carbon neutral. Achieving such an outcome requires measures advocated for decades, such as low-carbon fuels, vehicle and equipment efficiency, and modal shift. It remains unclear if carbon-neutral transportation is achievable in the medium term since it involves capital-intensive energy transitions. Modes such as maritime shipping have a much lower potential, mainly for technical reasons, as ship engines are massive. Technology other than the internal combustion engine cannot readily provide this power level. Urban transportation with a shorter lifespan of vehicles and a reliance on public transit has a better potential to become carbon neutral.

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Related Topics

• B.8 – Petroleum: A Transportation Resource
• 4.2 – Transportation and the Environment
• 4.3 – The Environmental Footprint of Transportation
• 4.4 – Transport, Sustainability and Decarbonization
• A.20 – Transport Environmental Management

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