The author of today’s post, Sheryl Canter, is an Online Writer and Editorial Manager at Environmental Defense.

Total greenhouse gas emissions from cars and trucks is a function of three factors: amount of driving, fuel economy, and carbon emissions per gallon of fuel (the "three-legged stool [PDF]"). The news media tend to focus on the latter two factors, but how much people drive has a huge impact.

A new report published by the Urban Land Institute says that greenhouse gas emissions cannot be reduced sufficiently by making vehicles more efficient, because growth in driving cancels out improved fuel economy. People also must drive less. And the report’s solution is not just better public transportation.

The way to reduce driving sufficiently, the authors say, is to shift development patterns to favor compact, mixed-land-use neighborhoods where you can walk to school and the grocery store. If you live in a car-dependent area, moving to a walkable area will do more to fight global warming than buying a fuel-efficient hybrid car.

This idea is already being put into action in some areas. New York City is expecting one million more people by the year 2030, and is using rezoning to direct development towards areas with strong transit access.

Environmental Defense helped California’s San Joaquin Valley, which is notorious for bad air quality, implement a similar strategy. The Air Pollution Control Board adopted an incentive program [PDF] that gives developers two choices: reduce the environmental impact by creating sidewalks, bike paths, and nearby schools and commercial districts, or pay a fee for any excess pollution.

Living in a walkable neighborhood has other advantages. Recently released figures from the New York City Department of Health show that New Yorkers tend to live longer than most people in the country — an odd finding considering the lack of fresh air and other hazards. The city’s Commissioner of Public Health thinks it’s because New York is a walking city.

By Mel Peffers, Project Manager of Environmental Defense Living Cities program

Cars in traffic in New York City

Last week, after Mayor Bloomberg announced his bold "greenprint" for New York City, Environmental Defense called for people to share stories about traffic. Arturo, a resident of Long Island City, Queens, New York, responded. He describes the perils of living on a busy high-speed thoroughfare:

"Trucks, buses, cars whiz by at high speeds. The green [light for drivers] is at least 90 seconds, perhaps longer, so vehicles are inclined to drive very fast. …. I play a game of chicken every time I cross. And during rush hours, other pedestrians like me are forced to jaywalk," he writes.

Besides the dangers of navigating traffic-choked streets on foot, Arturo's story illustrates dangers that are harder to see. "Soot accumulates on my windowsill and I clean that off on a regular basis. I was happy when I saw the local bus now employs hybrid-electric vehicles. My lungs will be thankful."

His story reflects the frustration and hope that many residents of vibrant, growing urban areas feel. Across the United States, city residents often face a daily dose of gridlock, smog and soot just going about their daily business.

Science has long shown that air pollution from trucks and cars is bad for your health. What's new is that over the last decade, scientists have looked more closely at street-level exposure and found a high-risk zone of about 500 to 1500 feet. If you live within that range of a heavily trafficked road, you face much greater risks than someone living farther away. The soot and fumes from cars, trucks and buses are linked to asthma, lung and heart disease and cancer. (More on how traffic is killing us.)

So how do we deal with future growth do if we already have problems now? Mayor Bloomberg's groundbreaking plan to make New York the world's cleanest, healthiest city can be a model for sustainable growth for cities across the country. How New York handles growth and achieves healthy air, less traffic, green buildings and energy efficiency — and more — will set an example for other cities around the world. (The director of our Living Cities program shares his thoughts on being on the mayor's advisory council.)

Part of the mayor's plan is a promising tool called congestion pricing. Places like London have used a pricing system to encourage less driving in the city at peak times, and achieved remarkable drops in both traffic delays and pollution. (More on congestion pricing and the results in other cities.)

We hope alarming stories like Arturo's about New York traffic are on their way out. But in the meantime, we'd like to hear from you, too. Do your kids go to school or play near a congested road? Tell us about your encounter with traffic.