, the authors explore the issues inherent in developing sustainable transportation. They review the types of propulsion systems and vehicle options, discuss low-carbon fuels and alternative energy sources, and examine the role of regulation in curbing emissions.

All technologies have an impact on the environment, from internal combustion engine vehicles to battery electric vehicles, fuel cell electric vehicles, and hybrids-there is no silver bullet. The battery electric vehicle may seem the obvious path to a sustainable, carbon-free transportation future, but it's not the only, nor necessarily the best, path forward. The vast majority of vehicles today use the internal combustion engine (ICE), and this is unlikely to change anytime soon. Improving the ICE and its fuels-entering a new ICE age-must be a main route on the road to zero emissions.

How do we go green? The future requires a balanced approach to transportation. It's not a matter of choosing between combustion or electrification; it's combustion and electrification. As the authors say, "The future is eclectic." By harnessing the best qualities of both technologies, we will be in the best position to address our transportation future as quickly as possible.