We all know the mantra by now: If you want to lose weight or prevent weight gain, you have to exercise along with eating healthfully. What kind of exercise? Why walking, of course. Your doctor mumbles something about walking three or four times a week while writing out the requisitions for lab tests at the conclusion of your annual physical. You want to ask how you are going to manage to do this under the blazing sun and humidity of the summer, or the dark, cold, icy, snowy days of winter, or on leaf-slick sidewalks after a November rainstorm. Or, if you can get another question in before being ushered out of the office, where are you going to walk since you live in a neighborhood without sidewalks?
Many cities or older suburban communities usually have sidewalks. They may not be free of snow in the winter, and cracked and jagged from old tree roots pushing up the pavement, but at least residents don't have to walk on the road. But this is not the case in many parts of the country where sidewalks and residential areas often part ways. If walking is to be done, it has to be on roads that often have no shoulders where one can stand to avoid being hit by a delivery truck or a mammoth SUV. If the side of the road has dense vegetation or rocks, even standing there may be perilous since there is little space for one's feet. More than once, I have stayed at a hotel /convention center for meetings in a suburban industrial park and have been forced to walk or run on highways with sand and pebbles flying in my face from passing trailer trucks. And although some suburban communities, often gated, have roads relatively free of traffic, the mind-numbing effect of walking round and round streets with only houses and not a store in sight is enough to send one inside.
Walking is the easiest, most convenient, and least expensive way to exercise, and there is data to support the notion that those who walk most may be the healthiest.  New Yorkers are supposed to be the fastest walkers in the country and may be among the healthiest. Today, the life expectancy of a baby born in New York is 80.9 years, which is 2.2 years more than the national average.  Of course, these city residents don't walk just for the exercise; it is often the most efficient and even fastest way for them to go from point A to point B.
The Bureau of Transportation Statistics reported several years ago that in the summer of 2002, 86 percent of the 205 million Americans walked at least once, and 40 percent walked more than 15 days, per month. The presence of sidewalks increased the tendency for adults to take walks, and the Bureau suggested that adding sidewalks to communities without them would increase the number by another 2.8 million. (In all fairness, some of these non-sidewalk communities may have walking trails or parks.) 
To be sure, there are many alternative ways of exercising: health clubs, home treadmills, recreational sports from skiing to swimming, dancing, rock climbing and more. All of these will certainly use up calories, increase stamina and bone strength and perhaps even cognitive acuity. However, unlike most of these other forms of exercise, except perhaps biking and rollerblading, walking permits multi-tasking which, in our overly busy lives, makes it a much more attractive form of exercise. Walking the dog, with your children to their school, to do errands, to the post office, to a doctor's appointment, to a neighbor, or to a movie, theater, concert or restaurant means that the walker is not only burning calories but also accomplishing some other goal. Indeed, there is a website called WalkScore that evaluates over 10,000 neighborhoods in 3,000 cities for their walkability, i.e., ease of doing errands and getting to recreational sites by foot.
Lifestyle change is the buzzword defining what has to happen if the obese are to become and remain thin, and the thin not to become obese. The ability to walk in safety, on sidewalks that lead to somewhere interesting, must be part of this healthy lifestyle if people are to follow it. Those who are fortunate enough to live in neighborhoods with sidewalks and places to walk to are aware of the positive impact this has on their lives. Social interactions are as likely to involve taking a walk as sitting and eating. Being out on the sidewalk has often led to friendships among neighbors who otherwise always leave the house in a car.
To be sure, having sidewalks and places to which to walk does not eliminate the discomfort and even hazards of bad weather, dog owners who do not clean up after their pets, and watching out for cars when streets have to be crossed. But it certainly makes it easier to respond to the suggestion to get out and walk, especially when it means you don't have to worry about finding a place to park your car.