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Transportation vehicles developed throughout the 20th century – autos, trucks and buses, airplanes and huge cargo ships – have been the single largest source of climate change and other forms of air pollution worldwide. Currently, these systems are responsible for about 40 percent of all greenhouse gas (GHG) emissions. While this fact is well understood, less evident to many people is the impact of the relationship between transportation and how land is used.

After the Great Depression and World War II these new forms of transportation powered by fossil fuels enabled an entirely different form of human development – suburban sprawl – which in turn requires the continued use of these new vehicles to serve those who live, work, shop and recreate there. This vicious cycle, with spread-out development patterns served primarily by automobiles, will continue to dominate the American landscape, and that of much of the developing world, for many decades. Even if all such development stopped tomorrow we would still be dealing with the environmental consequences – not only GHG emissions but other local air quality issues, significant loss of wildlife habitat and water quality problems caused directly by the spread of human development.

Our inner cities, largely developed in the era of the streetcar, the subway and the intra-urban train, use the land far more efficiently and allow people to walk from transit to wherever they need to go. The inner-ring suburbs developed in the streetcar era are now the most popular places to live because they have those same attributes. It’s the outer suburbs, and to a lesser extent residential development in rural areas, that are responsible for many of the serious environmental issues we face today.

Next time I’ll discuss the fiscal health of our communities – the third major crisis area.