The automotive industry is only in the early stages of the development and deployment of connected and automated vehicle (CAV) technology, but already an extensive body of research investigates the potential environmental impacts of these technologies. While this research is underway at leading universities, government agencies, and other organizations, currently very little real-world data demonstrates the environmental benefits of CAV technologies, and much of the evidence so far relies on simulations or pilot projects. Thus, to a large extent, both the magnitude and direction of the future impacts remains uncertain and amenable to change depending on how this technology is adopted and used.

On the plus side, we can point to several paths by which CAVs can help mitigate the environmental impacts of the transportation system. These include smart routing, self-parking, and eco-driving (making optimum driving decisions and smoothing the acceleration cycle), all of which have the potential to reduce tailpipe emissions (NOx, SOx, and CO2) and lower overall fuel consumption. Other energy and environmental benefits of CAVs could include decreased life-cycle energy consumption and reduced GHG emissions from infrastructure that can mitigate the urban “heat island” effect.

The energy and environmental impacts of light-duty CAVs depend on several interdependent variables: level of vehicle automation; vehicle weight, size, and propulsion technology; travel demand; and supporting infrastructure. Some vehicle automation features, such as platooning, eco-driving, enhanced vehicle performance, and improved crash avoidance, either enable or complement CAV technology, and the combination of these features could considerably decrease overall vehicle energy consumption. CAVs might also prove to be more fuel efficient with lower emissions through efforts to reduce the overall mass of the vehicle or by shedding unnecessary weight with the omission of entire components for human control such as the steering wheel or brake pedal. Vehicles designed exclusively for cargo or other non-passenger uses might offer an even greater opportunity for vehicle lightweighting because these vehicles do not require the convenience, comfort, and safety features designed for vehicle occupants. Furthermore, electric vehicles (EVs) likely are easier to recharge or refuel without a human operator present, and CAVs that are EVs also can reduce emissions.

Travel behavior and innovative mobility services (such as ride-haling and car-sharing) will also affect the environmental benefits of CAVs. Without significant changes in current travel behavior and associated vehicle occupancy rates hovering around 1.08 for many trip types, CAVs also have the potential to make the environmental problems of vehicle travel worse. Every single-passenger ride-hailing trip has the potential to produce more emissions and more congestion than a transit trip or even a singly occupied vehicle. This would occur from two primary sources. First, increased vehicle miles traveled (VMT) could accumulate from ride-hailing vehicles deadheading from one drop-off point to the next pick-up point. Second, VMT also could increase by moving trips from transit to ride-hailing. If true ride-sharing comes to pass—meaning trips consisting of two or more passengers—then the potential for environmental benefits expands. There is very little evidence, however, that tolerance for out-of-vehicle wait time—a key variable working against transit and other shared modes currently—is increasing.

New transportation infrastructure specifically designed to leverage the unique benefits of CAV technologies might provide significant benefits. With advanced traffic management powered by artificial intelligence, CAVs can reduce the need to expand existing infrastructure by increasing throughput on current roads and highways. CAVs also might require fewer and smaller parking spaces and travel with less distance between cars, thereby using existing infrastructure more efficiently. If this induces more traffic, however, then the benefits might be lost.

Ultimately, assessing the environmental impacts of CAVs will require real-world data and consideration of interactions between CAVs, EVs, travel behavior, and the infrastructure, and these interactions could drive the net environmental effects of CAVs in a positive or negative direction. To better understand the future transportation system with CAVs, researchers need to carefully evaluate the feasibility of various deployment scenarios and the scale of the environmental, economic, and societal changes in each scenario, as well as to follow real-world trends to assess the likelihood that each scenario might come to pass.

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