The United States is the largest emitter worldwide of the greenhouses gases that cause global warming. Transportation accounts for a full third of CO2 emissions in the United States, and that share is growing as others shrink in comparison. Automobile emissions continue their rapid rise in large part because we have built our cities so that we have little choice but to drive from activity to activity.

It is hard to envision a "solution" to climate change and energy security that does not involve slowing the growth of our transportation emissions. To date, the national discussion of energy and climate initiatives has focused almost entirely on developing more fuel-efficient vehicles or lower-carbon fuels. Experts acknowledge, however, that all foreseeable technological solutions are sure to be overwhelmed by the continued growth in the number of miles we all drive.

The good news, though, is that we can make enormous progress simply by shaping future building so that we create more communities where people can accomplish more by driving less. Numerous studies now demonstrate that when people are given the option to live in a less automobile-dependent place, they do indeed drive less.

According to the groundbreaking report Growing Cooler: The Evidence on Urban Development and Climate Change, residents of more compact neighborhoods drive 20-40 percent less on average—and less driving equals less emissions.

If you combine that effort with increased investment in public transit of all shapes and sizes, we can reduce dangerous emissions even more.

Vehicle Miles Traveled (VMT) and land consumption rates are rising rapidly

After the Arab Oil Embargo of 1973 highlighted the fragility of depending on foreign oil, automakers began to consider better fuel efficiency and our average miles-per-gallon rates rose for the first time in years. The improvement in efficiency has been overwhelmed by the sheer increase in the miles we drive, thanks to our increasingly spread-out, automobile dependent development patterns.

Where does my state rank? Click to view the graph and access detailed state-by-state VMT data

Since 1973, due in large part to our development patterns, Americans are traveling 250 percent more miles each year.

As our landscapes have become more suited for automobile travel only, the amounts of driving necessary to navigate them have been increasing at alarming rates. Development has become more spread-out, with land consumed for development at twice the rate of population growth during a 20-year period from 1982-2002. Per-capita vehicle miles traveled (VMT) per person has increased three times that of America's population growth over that same period.

It's no accident that VMT is increasing as we continue to build and develop more areas where residents have no realistic choice but to drive long distances each day to reach their daily needs. A study published by SGA in 2002 found that the degree of sprawl was the greatest link to a high quanity of vehicle miles traveled. (Measuring Sprawl and Its Impact)

© 2007 David Horsey/Seattle Post-Intelligencier

Energy consumption and our reliance on oil threatens our national interests and security

The cold hard truth? We don't produce enough oil to meet our own demand—which is rising every year.

The United States currently produces 8.9 million barrels of oil a day, representing only 40 percent of what we consume on any given day (21 million barrels.) A sizable percentage (22%) of our imports come from an unstable Persian Gulf region. Half of our imports come from OPEC member nations. As demand continues to grow—which currently shows no sign of slowing—we will become more reliant on importing oil each year. Imports, which currently supply 2/3 of our daily needs, could rise to as much as 3/4 by 2030 based on current rates of consumption.

It's not only us. Other developing countries like China and India are witnessing huge spikes in the rates of car ownership, and we will be competing with many other countries for a limited supply of imports, becoming more expensive all the time.

Domestic refineries operate at near-capacity, and small disruptions in the supply line can have disastrous consequences on our national economy that requires abundant oil to survive day-to-day. It doesn't take a terrorist act to damage our national security—natural disasters alone can do it. We saw some of this fragility firsthand when Hurricane Katrina knocked refineries offline and cut down supply in some southeastern states. Georgia Governor Sonny Perdue cancelled school after Katrina in an attempt to cut down on driving as gas prices rose to historic levels.

Increases in driving brought on by land-use patterns contribute to global warming.

The "Three-Legged Stool"

Cleaner, more efficient technology for vehicles—though needed and useful—will not be sufficient solutions on their own

Increases in fuel efficiency have not been able to keep pace with the increases in driving, resulting in net increases in emissions even as efficiency has improved. Many proposed solutions include plans for renewable energy, lower carbon fuels, or more efficient vehicles—largely overlooking an obvious component: our ever-growing reliance on driving.