Since the energy crises of the 1970s the U.S. has struggled to substitute alternative energy
sources for petroleum use by motor vehicles. This report reviews recent studies of a wide range
of policies to promote alternative fuels and vehicles to extract insights about their impacts and
effectiveness. Although the emphasis has varied over the past four decades, the motivations for
replacing petroleum fuels have remained the same:
- Prevent or mitigate dangerous changes in the global climate by substituting low-carbon
energy for fossil petroleum. - Improve energy security by reducing national dependence on petroleum.
- Improve local air quality by eliminating or drastically reducing emissions from motor
vehicles.