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Notwithstanding the brutal winters of Montreal, I can proudly state that I live in a highly walkable city. The teaser image (also shown here) is of a pedestrian street in Montreal called Prince Arthur. Montreal is replete with such neighborhoods. Both North American and European urban design philosophies have influenced the city's urban planners, and as such this has yielded one of the most livable cities in the world. On the other hand, many American cities (especially the downtown areas) are extraordinarily inhospitable, and certainly so after business hours (see the image of a 
typical Detroit vista). Of course, the United States has its fair share of walkable towns including New York, Boston, and Seattle.
The suburbia effect has created urban sprawls that have a profound negative effect on one's health let alone one's aesthetic sensibilities and joie de vivre. Several studies (cf. Tomalty & Haider, 2009; Frank et al., 2006) have demonstrated that people who live in more "walkable" neighborhoods are thinner and healthier than their counterparts who live in less walkable areas. Of course, researchers control for possible confounds such as socioeconomic variables, as a means of isolating the effect of a neighborhood's walkability index on health outcomes. There are many ways to create such an index but typical variables include the presence/absence of sidewalks, the width of the sidewalks, the proximity to green spaces such as parks, the number of trees lining the streets, the average lengths of blocks, protection from inclement weather, a feeling of safety, dimensions that are human-scaled (rather than car-scaled), the average width of streets, the density of people, and the heterogeneity of housing styles.
From a public policy perspective, this suggests that more effort should be spent on designing healthy urban environments that promote a more active lifestyle. One of the explanations for the so-called French Paradox is that the French tend to walk much more than Americans do, precisely because their cities are so much more walkable. Whereas going to the gym and watching your food intake are important measures, a healthy urban environment can also do wonders to an individual's overall health.
For those of you interested in reading more about our innate preferences for particular urban and natural landscapes, be on the lookout for my forthcoming trade book to be published in 2011, as I discuss the issue in much greater detail. Happy walking!
Sources for Images:
http://i.rentalo.com/images/Montreal-Apartment-Condo-p4_202024_455249l…
http://2.bp.blogspot.com/_2uL9b4oOkoY/SUQ1jUEqIfI/AAAAAAAAGI0/bmrlFW4vr…
