  Connected and automated vehicles (CAVs) are poised to reshape transportation
and mobility by replacing humans as the driver and service provider. While the
primary stated motivation for vehicle automation is to improve safety and
convenience of road mobility, this transformation also provides a valuable
opportunity to improve vehicle energy efficiency and reduce emissions in the
transportation sector. Progress in vehicle efficiency and functionality,
however, does not necessarily translate to net positive environmental outcomes.
Here we examine the interactions between CAV technology and the environment at
four levels of increasing complexity: vehicle, transportation system, urban
system, and society. We find that environmental impacts come from
CAV-facilitated transformations at all four levels, rather than from CAV
technology directly. We anticipate net positive environmental impacts at the
vehicle, transportation system, and urban system levels, but expect greater
vehicle utilization and shifts in travel patterns at the society level to
offset some of these benefits. Focusing on the vehicle-level improvements
associated with CAV technology is likely to yield excessively optimistic
estimates of environmental benefits. Future research and policy efforts should
strive to clarify the extent and possible synergetic effects from a systems
level in order to envisage and address concerns regarding the short- and
long-term sustainable adoption of CAV technology.
