Walkable cities prioritize two feet over four wheels through careful planning and design. They minimize the need to use a car and make the choice to forego driving appealing, which can reduce greenhouse gases emissions. According to the Urban Land Institute, in more compact developments ripe for walking, people drive 20 to 40 percent less.
Walkable trips are not simply those with a manageable distance from point A to point B, perhaps a ten- to fifteen-minute journey on foot. They have walk appeal, thanks to a density of fellow walkers, a mix of land and real estate uses, and key design elements that create compelling environments for people on foot. Infrastructure for walkability can include:
- Density of homes, workplaces, and other spaces.
- Wide, well-lit, tree-lined sidewalks and walkways.
- Safe and direct pedestrian crossings.
- Connectivity with mass transit.
Today, too many urban spaces remain no- or low-walking ones, and demand for walkable places far outstrips supply. That is because walkable cities are easier and more attractive to live in, making for happier, healthier citizens. Health, prosperity, and sustainability go hand in hand.
Project Drawdown defines walkable cities as: designing and retrofitting urban environments to encourage walking for commuting or transportation. This solution replaces the conventional practice of driving internal combustion engine (ICE) cars in cities.
Walking is the most neglected mode of transportation: the simplest, most sustainable, and cheapest medium of locomotion. In 2014, humanity walked 1,523 billion kilometers, or an average of 200 kilometers (130 miles) per person per year – barely 7 minutes per day. We drive 7 times as much as we walk. Walkability is still associated only with leisure and recreation in the majority of urban projects around the world; however, the notion of walking as a competitor in the area of sustainable urban mobility is increasing.
Walkability has commonly measured according to the “7Ds”: 1) Density of activity, 2) Diversity of land uses, 3) Design of the street network, 4) Destination accessibility by distance or time, 5) Distance to transit, 6) Demand management, and 7) Demographics (which is not part of the built environment, but still important). These D’s influence patterns in travel choices based on the characteristics of users. Because there is insufficient measurement of all variables for large numbers of cities, this analysis focuses on population density as the key indicator for walkability. 
The six dimensions of the built environment—demand, density, design, destination, distance, and diversity—are all key drivers of walkability. Our analysis focuses on population density as a proxy for walkable neighborhoods. As cities become denser and city planners, commercial enterprises, and residents invest in the “6Ds,” 5 percent of trips currently made by car can be made by foot instead by 2050. That shift could result in 2.9 gigatons of avoided carbon dioxide emissions and reduce costs associated with car ownership by $3.3 trillion.