"Living in a mixed-use neighborhood -- with a mixture of single family homes and multi-family housing, with some stores, transit, and other services nearby -- might cut the average person's driving by perhaps a third to a half, compared with car-dependent sprawl. Living in an even more compact urban neighborhood, with lots of stores and jobs within walking distance, might cut per capita driving by a half to two-thirds, or perhaps more.
At the level of an entire metropolis, the effects of compact design can be signficant. The report found that Portland's metropolitan land use and transportation planning system, in place since the 1970s, has cut city residents' driving by 17 percent. Just so, residents of the comparatively compact Boston metro area drive a quarter less than do folks in sprawling Atlanta."
The layout of a city has effects for many many years and thus can significantly impact that cities greenhouse gas emissions.
There is some pessimism about the value of changes that take so long to make a significant impact. Here is Mr. Williams-Derry's take on that;
"As I see it, there are at least 5 major reasons why we shouldn't settle for the more pessimistic view.
1) We should think on the margins: A metro area's population might grow only a percent or two a year, so the averages don't budge much year-to-year. But on the margins, encouraging new development in denser areas turns out to be a very effective way of reducing the greenhouse gas emissions from new residents. Over the long haul, it's the margins that matter, since they control the direction of change.
2) There's more to emissions than how much we drive: Reductions in driving understate the climate benefits of compact neighborhoods. As this study shows, living in a compact neighborhood doesn't just reduce how many miles you drive, it also seems to increase the odds that you'll choose a more fuel efficient car. And compact neighborhoods can also reduce net emissions for heating, cooling, and powering your home.
3) Creating alternatives to sprawl has multiple benefits. Channeling growth into compact neighborhoods can help protect farmland and open space; reduce wasteful spending on public infrastructure; promote health; reduce impervious surface per capita; and so forth. As important as greenhouse gases are, it's only one reason among many for curbing sprawl.
4) Waiting for the feds is a sucker's game. Cities and towns that want to take action to protect the climate simply can't sit back and wait for federal action on, say, boosting auto fuel efficiency. Waiting for the feds is the lazy way out -- and given the ever-changing nature of politics, it's an incredibly risky strategy, since even the most progressive federal policies can change overnight.
5) Over the long haul, even small things matter--a lot. Global warming is a long-term problem, and it requires long-term solutions. Sure, it could take 50 years or more for changes in urban form to take a major bite out of US emissions. But if the developed world is going to make the massive emissions cuts that are going to be necessary, we're going to have to employ every single tool at our disposal."
I can speak from personal experience having now lived in the very walkable city of Sheffield England and am now living near the city center of Hamilton Bermuda, no car needed in either. It is an absolute joy! My quality of life is so much higher than when I lived in cities with planning centered around the automobile. I used to spend up to an hour or more driving every day, what a waste of time. Now I walk every day, either for my usual errands or intentionally for exercise, and as a result don't need a gym membership or any exercise equipment taking up room in my home, I don't have car payments, don't buy gasoline, pay for auto insurance, maintenance or tires. So for me living in a walkable neighborhood is a quality of life issue and it certainly reduces my personal carbon footprint.