Intergovernmental Panel on Climate Change (IPCC) research suggests that the world needs to reduce global greenhouse gas emissions by 45% by around 2030, and achieve net-zero emissions by 2050, in order to avert the worst impacts of climate change. However, meeting such long-term goals will require deep cuts in emissions in the coming decades, including in transportation where emissions are projected to increase significantly by 2050, absent new actions.
In 2020, COVID-19-induced shutdowns led to rapid declines in transportation emissions, as people stopped commuting and travel, and many businesses were forced to close. In areas with tight lockdowns, road transport saw declines as high as 50% to 75% in the spring. Meanwhile, freight transport declined somewhat, while passenger aviation demand plummeted. As the coronavirus pandemic persists, it remains to be seen how quickly economic activity and pre-pandemic transportation trends re-emerge, particularly in hard-hit countries like the United States, Brazil, and India. However, underlying fundamentals of the transport sector have not changed, and in the United States, as states slowly lifted restrictions in May and June, road, aviation, and shipping transportation emissions began to rise once again.
In new Brookings research, Samantha Gross examines key challenges to decarbonizing heavy transport, including heavy-duty freight, maritime, and aviation. Several observations emerge:
Global transportation emissions continue to grow.
Transportation accounts for approximately one-quarter of global greenhouse gas emissions, and emissions continue to rise. Pre-pandemic, transport made up 29% of global primary energy use and 25% of global energy-related carbon dioxide emissions. In the United States, transportation is the largest source of greenhouse gas emissions, with 29% of the total. The transportation sector has not benefitted from the tailwinds that have reduced GHG emissions in the electricity sector, namely, plummeting prices for renewable electricity and inexpensive natural gas in the United States. In 2017, the transportation sector made up 27% of emissions in the EU and is the only main European economic sector in which GHG emissions have increased compared to 1990 levels.
In middle-income and developing countries, lower ownership of personal vehicles and smaller distances traveled result in lower GHG emissions from transportation than in more developed economies, totaling 8.6% of total emissions in China and 12% in India. Still, global transportation emissions have more than doubled since 1970, and transport emissions are projected to continue to rise at faster rates in these countries than in the developed world, as consumer demand for personal transport rises. Heavy-duty transport is among the fastest-growing sectors. Although the coronavirus pandemic brought significant declines in transportation emissions, as economic activity resumes, demand is again expected to rise, particularly in the developing world. The figure below shows the increasing share of transportation sector greenhouse gas emissions in countries outside the OECD over time.
The transition away from oil in light vehicles has begun but heavy transportation lags behind.
Cars, light trucks, and two-wheelers are the easiest place to start in decarbonizing the transportation sector, and that transition has already begun. From 2011 to 2018, EV sales in the United States grew 91%, and the International Energy Agency projects that there will be 125 million electric cars on the road by 2030. Longer-term estimates of EV sales vary considerably, based on assumptions about policy and technology. Low-penetration scenarios call for 305 million passenger EVs by 2040, 15% of the global fleet, while very optimistic scenarios call for as many as 900 million EVs by that time, accounting for nearly half of the fleet. While estimates of electric vehicle growth vary, there is consensus that increased cost-competitiveness and government regulations will push both supply and demand.
Electric vehicles and greater efficiency in vehicles with internal combustion engines are reducing the oil consumption of the light vehicle fleet. The International Energy Agency estimates in its New Policies Scenario that oil demand from light vehicles will peak in the early 2020s, despite strong growth in the number of vehicles on the road. Efficiency improvements are the most important contribution to this trend in the near term, with fuel substitution, especially electrification, also contributing. Electric vehicles are currently leading the race to remake the light vehicle fleet, but other technologies, especially hydrogen fuel cells, also have great potential.
In the United States, cars and light trucks accounted for 55% of U.S. transportation energy use in 2017. Commercial and freight transport accounted for 24%, non-highway transport for 22%. The breakdown between on-road and nonhighway transport is similar in Europe, where 82% of transport energy use is on the road.
However, displacing oil in the non-light vehicle portion of the transportation sector is more difficult. In heavy trucking, shipping, and aviation, moving people or goods over long distances makes the energy density of fuel particularly important. The energy density of batteries is orders of magnitude lower than petroleum fuels, making heavy transport more difficult to electrify. For these sectors, lower carbon fuels that mimic the useful characteristics of petroleum fuels are a promising pathway for decarbonization. Biofuels or fuels produced using electricity, such as hydrogen and synthetic fuels, are the likely substitutes in long-distance transport, but these fuels have their own inherent limitations. Since liquid fuels are so important in these sectors, minimizing liquid fuel use in light transportation (and in other sectors of the economy) will be crucial to saving those fuels for where they are most needed. This issue is especially important in the case of biofuels, where land use constraints limit their production.
Unfortunately, the harder-to-abate portions of transportation are also among the fastest growing. The International Energy Agency estimates that oil demand in aviation will increase more than 50% and in trucking by 25% by 2040. In these sectors, a number of strategies will be needed for decarbonization.
Substitution with lower carbon biofuels, hydrogen, or synthetic fuels made with captured CO2 are options. But the expense and land use implications (in the case of biofuels) of these fuels means that efficiency improvements and changes to vehicle operation will be needed to keep overall costs down.
Barriers to decarbonizing heavy transport persist.
Ideal transportation fuels are energy-dense, meaning they contain a great deal of energy per unit of weight or volume. In heavy-duty transport — such as trucking, shipping, and aviation — moving heavy goods or significant numbers of people long distances make the energy density of the fuel important, as the fuel must be carried along with the load. In aviation and shipping, there are often no re-fueling options mid-trip. For these reasons, heavy transport still remains reliant on oil, with the International Energy Agency estimating that oil demand in aviation will increase more than 50% by 2040, and 25% in trucking.
Using today’s fuels, efficiencies can be gleaned through upgrading to more efficient vehicles and route efficiencies such as freight corridors. Several countries have now developed heavy-duty vehicle fuel efficiency standards, including the European Union, Mexico, Japan, the United States, Argentina, and Canada.
Emerging technological opportunities expand possibilities.
Improvements in diesel truck technology raise the bar that new decarbonized technologies must meet to be competitive. Electrification is a good option for medium- and heavy-duty vehicles that operate in limited areas and follow set routes, since they can refuel frequently at a central location. Buses are the low-hanging fruit; more than 136,000 electric buses were sold in 2019, mostly in China. The city of Shenzhen has entirely electrified its fleet of more than 16,000 buses. Urban delivery vehicles, drayage trucks and other vehicles at ports, and service vehicles like garbage trucks are other relatively easy targets for electrification. Amazon has committed to purchasing 100,000 electric delivery vans from Rivian, with delivery starting in 2021.
For long-haul electric trucks, range and payload are the primary and interrelated challenges. Batteries are heavy compared to liquid fuel — extending the truck’s range with extra batteries takes away from the weight of freight that it can haul. Long-haul Class 8 trucks, like tractor-trailers, or semi-trucks, have a total weight limit of 80,000 pounds, including the vehicle and payload. A battery with 500 miles of range would add 10,000 pounds to the vehicle weight, a substantial cut in hauling capacity. Raising the weight limit somewhat for electric trucks could help with this challenge, as could a smaller battery, resulting in shorter vehicle range.
Electric heavy-duty trucks also pose charging challenges. Because they will have much larger battery storage than an electric passenger vehicle, they will also require more power for charging. Fast chargers for personal vehicles deliver 50 to 150 kilowatts (kW) of electricity, charging a vehicle completely in roughly 30 minutes to two hours, depending on the battery size and charging rate. (Level 2 home chargers deliver around 10 kW, for four to 10 hours of charging time.) The scale changes completely for large trucks. Battery sizes as large as 1000 kW-hours require very high-power flows to charge quickly. A light vehicle fast charger could take as long as 20 hours to charge such a large battery. Overnight charge times might be fine for many local applications but raise a serious challenge for long-haul trucking.
Chargers with very high rates are one potential solution. Chargers rated as high as 3 MW, or 3000 kW, are in development for heavy duty trucks. These have the advantage of charging trucks in a similar time to refueling with diesel, making long-haul battery trucks more economic for hauling companies, since time is money in this application. However, these chargers have serious implications for the power grid, particularly if there are several of them in a single location, such as at a highway truck stop. This high level of discontinuous, “lumpy” power draw is a challenge for the grid and will require battery storage or distributed generation to balance the load. Proactive grid expansion of electrical infrastructure at designated truck charging stops would be needed as such heavy trucks are deployed. Slower chargers lighten the load on the power grid but raise challenges of land use and space to accommodate trucks for the longer charging time, in addition to the economic challenge of more downtime for refueling.
Charging along a route is an additional possibility for electric heavy vehicles. Applications of wireless charging technology are already in use in fleets where vehicles follow a set route. For example, in California, the Antelope Valley Transit Authority operates a fleet of electric buses with 250 kW inductive charging pads in the pavement at some transit centers. The all-electric buses can top off their batteries during planned longer stops at these centers, meaning that they can run for the same number of hours per day as the diesel buses they replaced. This technology is more difficult for large vehicles that need route flexibility, like long-haul trucks. Wireless charging imbedded in road surfaces or charging from overheard wires are both possible but require very large infrastructure investments. Such infrastructure could be built on main shipping routes, with vehicles relying on battery storage for “last mile” travel on smaller roads.
In addition to electrification, alternative fuels could provide pathways to decarbonization. Biofuels and other liquid fuel types that are compatible with today’s infrastructure and engines provide an easy pathway. However, these types of fuels are more needed in the harder to decarbonize aviation and maritime sectors. Diesel made from agricultural products or waste is blended into some fuel today, for compliance with the Federal Renewable Fuels Standard and the California Low Carbon Fuel Standard. Even if road transport is not the highest and best use of these fuels over time, regulations for the trucking industry are encouraging development and scale-up of the technology.
Hydrogen is another alternative fuel that has potential in trucking. Hydrogen-fueled trucks have electric drivetrains and use the hydrogen to produce electricity in a fuel cell. Thus, these trucks have many of the same advantages as electric vehicles — a lighter, simpler, and more efficient drivetrain — without the disadvantage of the heavy battery and long refueling time. However, the hydrogen truck market is less advanced than that for electric trucks, primarily because of the need for extensive infrastructure to produce and distribute hydrogen. Also, to achieve its potential, hydrogen for trucking would need to be produced by splitting water molecules through the process of electrolysis, using renewable electricity, rather than the process of steam reforming methane that is more common today. Nonetheless, hydrogen trucks are under development. Kenworth and Toyota are partnering to develop a hydrogen-fueled Class 8 truck,79 Cummins has hydrogen trucks in development,80 and start-up Nikola has hydrogen trucks on the market today.
In addition to the technology, the fragmented structure of the long-haul trucking industry raises challenges for decarbonization investments. In the United States, a strong majority of trucks are owned by companies that operate 20 trucks or fewer. In Asia, nearly 90% of trucks are owned by individual drivers. Smaller companies are less able to take risks on new technology or provide dedicated refueling infrastructure, and they have less access to capital to cover up-front costs of trucks and changing technology. Smaller companies are also less likely to face public pressure to take the lead in new technology, since they are not household names and are often privately owned, and thus do not face pressure from shareholders or investors. Smaller companies operate in a competitive market with thin margins.
Many of these technologies are expensive or untested at scale, pointing to the need for public-sector investments in research and development to spur private-sector innovation. Additionally, technology-neutral policy standards, like zero emissions vehicle requirements, are useful policy levers. Policymakers must strike an important balance between reducing emissions today, while also supporting the continuing development and piloting of new technologies and next-generation fuels.
The full report can be accessed by clicking here