It's not just enough to encourage people to walk: as Tom Vanderbilt shows, decades of planning for high-speed automobility have made walking almost impossible in some parts of metropolitan areas.
"A large part of the problem is that places...were built on the idea that there wouldn't be anyone walking on them. Indeed, there wouldn't be much of anything happening on them, except for cars speeding uninterruptedly from one dense town to another. This was the vision articulated by early optimists like Benton MacKaye and Lewis Mumford, who sounded their call for such roads in a 1931 Harper's article called 'Townless Highways for the Motorist.' Not only should highways avoid the centers of towns, they argued-in order to keep long-distance traffic from congesting already-busy urban thoroughfares- but those highways should themselves be free of commercial development.
[But] the high-speed suburban arterial became a kind of American Main Street...What's more, these arterials were typically built without any provisions for people walking-because who would be? [Pedestrians] are as invisible to society as they are to the average driver. This failure to plan for anyone on foot is just one of a number of shortcomings of our overbuilt, undermaintained road network that are coming into relief."
Instead of laying streets and planning for sidewalks later -- as has been the practice in many developments - Vanderbilt shows how more than 300 municipalities are now planning for "complete streets" that facilitate multiple modes including walking.