Deep Decarbonization and Transportation Engineering

It is easy to argue that the transportation field will see more changes in the next 10 years than we have seen in the past 80 years. The innovations leading these changes include automated and connected vehicle technology and electric vehicles technology. One of the motivating factors behind the adoption of these technologies is that many governments and firms have made pledges to reduce greenhouse gas emissions (GHG) over the next decades (NASEM 2021a). These commitments reflect the scientific consensus that increasing GHG concentrations in the atmosphere are causing climate change, which is characterized by rising average global temperatures and increasing extreme weather events. Economic and social costs from climate change are already apparent with rising sea level and droughts. Net zero GHG emissions is often cited as a goal to halt these climate change effects. Net zero emissions means the amount of greenhouse gas produced and the amount removed from the atmosphere through carbon capture and sequestration are equal. Because carbon dioxide (${\mathrm{CO}}_2$) is the largest GHG emission, net zero goals are often termed deep decarbonization. In 2019, the transportation sector was the largest source of GHG emissions in the United States at 29%, with the vast majority ${\mathrm{CO}}_2$ with much smaller amounts of methane (${\mathrm{CH}}_4$), nitrous oxide (${\mathrm{N}}_2$), and hydrofluorocarbons (HFC) (EPA 2022).

In a journal devoted to improving transportation through better engineering, it is worthwhile to consider the implications of deep decarbonization for transportation engineering.

As explored for many decades, a variety of actions can be employed to reduce GHG emissions in transportation (Deakin 2011). Currently, the bulk of vehicle travel is by internal combustion engine vehicles (ICEV) with gasoline and diesel as the primary fuel sources. While the efficiency of ICEV has continued to improve over the years, thanks to better computer control, materials, and fuel and air handling, it is clear that these improvements will not lead to a net-zero future. Ironically, even the catalytic converter, which is designed to improve air quality, produces the GHG nitrous oxide, which is approximately 300% more potent than ${\mathrm{CO}}_2$. Electrifying vehicle propulsion coupled with carbon-free power generation can reduce transport GHG emissions as well as conventional air pollutants such as particulate matter from diesel vehicles. Battery electric (BEV) and fuel cell (FCV) vehicles are already commercially available.

Another GHG reduction strategy is to encourage people to use nonmotorized modes such as walking or cycling, to share rides, and to eliminate trips altogether. Investments in infrastructure for better telecommunication and for sidewalks and bike paths can help this strategy succeed. Targeting public transportation for energy efficiency can also be a useful strategy.

Reducing embedded emissions in infrastructure can also help, such as using waste materials or low carbon cement in concrete. It has been found that lifetime GHG emissions associated with asphalt concrete pavement construction can be reduced between 50% and 65% if reclaimed asphalt pavement is used (Bizarro et al. 2021). Low carbon fuels can replace fossil fuels for uses such as aviation. Pursuing deep decarbonization will require numerous actions, many extending beyond transportation engineering. In this editorial, we will focus on transportation engineering issues and encourage technical and professional engineering articles on the planning, design, construction, operation, and maintenance of air, highway, rail, and urban transportation systems and infrastructure (Hendrickson and Rilett 2019).

Operational changes on roadways can also reduce GHG emissions. For example, connected and automated vehicles have the potential to improve overall traffic flow. Truck platooning has been shown to have aerodynamic, and hence fuel-saving, advantages.

Freight logistics will be significantly affected by deep decarbonization. New industries are likely to develop, such as public charging stations and vehicle battery manufacturers. Renewable power sources from solar and wind will be more distributed than fossil fuel power plants, such as rooftop solar installations. Agriculture may be used for biofuel crops or carbon sinks and urban agriculture can reduce freight demand. Distributed three-dimensional printing may be used for producing goods locally, which will reduce the need for multicountry supply chains. Digital distribution of music and films is already widespread. Shifting freight movements from air and truck to more energy efficient ships and trains for at least part of a trip is also a possible strategy.

Equity impacts and issues arise in pursuing deep decarbonization. Employment will decline in fossil fuel industries as vehicles become electric and the power grid reduced GHG emissions. New industries should emerge, but there will be transition impacts and need for new training. It is important that deep decarbonization policies do not inequitably burden communities that have been historically disadvantaged by past transportation policy.

From this brief summary of actions to move toward deep decarbonization in transportation, there are numerous challenges and opportunities for transportation engineers. In the subsequent paragraphs, we suggest some of the areas of interest.

Electric vehicles have continuing research and innovation challenges (NASEM 2020, 2021b). BEV and FCE vehicles have similar vehicle sizes and performance as existing conventional vehicles, although the instant torque and lighter weights associated with BEV can change vehicle maneuvering. At the same time, highly automated and connected vehicles will also change traffic flow characteristics. Trip-making with BEV must consider the range available from the vehicle battery and the availability of wayside charging on long trips. Vehicle components, charging infrastructure, and trip-making with BEV will be significant concerns for transportation engineers.

Roadway and other transportation infrastructure need not change extensively, except for the introduction of charging infrastructure. Charging stations will be needed near roads, along with power transmission and distribution infrastructure. Some charging may be embedded in roadways. Roadway right-of-way may be useful for power and communications transmission lines investments in charging infrastructure are already increasing as sales of BEV increase.

Efficiency improvements to reduce vehicle miles traveled (VMT) or to reduce emissions from conventional vehicles can help reduce GHG emissions. Efficiency has been pursued for many decades by transportation engineers, but improvements are still possible. Connected and highly automated vehicles are a good example. Connectivity might be used to aid traffic flow in a variety of ways. Safety improvements with automated vehicles can reduce traffic congestion from crashes. Shifting trips to shared rides or active modes such as biking and walking can reduce VMT. Improved route planning for delivery vehicles can also help. Efficiency improvements will continue to be a major concern for transportation engineers.

Efficiency improvements can have many benefits other than GHG reductions. For example, travel costs can be reduced with congestion reduction improvements or improved conventional vehicle fuel efficiency. Transportation engineers should be cognizant of the benefits and costs of efficiency actions over the life cycle of vehicles and infrastructure. One useful tool in cost effectiveness analysis is an implicit cost of GHG emissions. A cost of $40/t ${\mathrm{CO}}_2$ equivalent in 2021 and rising 5% per year has been suggested for deep decarbonization and could be used in cost effectiveness studies (NASEM 2021a). Of course, transportation engineers must also consider other goals such as equity and safety in planning, design, and operations.

While the process of deep decarbonization occurs or if it does not happen, transportation engineers must contend with the effects of climate change. Sea level rise and extreme weather can affect all transport infrastructure and operations. Coping with wild fires and mudslides is already creating problems for infrastructure operations in many areas, especially in the western United States, while hurricanes and flooding from extreme storms is a nationwide problem. Infrastructure resiliency with be increasingly important over the next decades. This will include how to make our infrastructure more resilient to these events (e.g., pavement that can survive flooding) as well as operating our system to allow for large-scale evacuations while simultaneously allowing access to affected areas by first responders.

In summary, transportation engineers should be aware of the requirements of deep decarbonization and the response to climate change. As discussed in this editorial all aspects of the planning, design, construction, operation, and maintenance of air, highway, rail, and urban transportation systems will be affected. Government and industry leaders should be proactive on these impacts. Researchers face numerous challenges as well. While the focus of this editorial is on US options, other countries face the same issues. US transportation systems engineering should be adapted to prepare for this transition with research directed to making it as smooth as possible.

As in the past, the Journal of Transportation Engineering, Part A: Systems stands ready to publish articles exploring the link between communications and transportation.