California's natural and biological resources are essential for the environmental and economic health of the state. Ninety-five percent of California's wetlands have vanished over the last two centuries, thirty-two percent of California's native plant species are currently at risk (the highest percentage of any state in the continental U.S.), sixteen percent of the oak woodlands in the foothills of the Sierra Nevada have been lost, and twelve percent of the Central Valley's prime farmland has been paved over.

Transportation policies, by facilitating growth into farmland and natural areas, have played a role in this loss of natural habitat, and will continue to influence the environmental health and habitat diversity found throughout the state for decades to come. Transportation is also a significant source of both air and water pollution.