Walkability is a measure of how friendly an area is to walking. Walkability has many health, environmental, and economic benefits. Factors influencing walkability include the presence or absence and quality of footpaths, sidewalks or other pedestrian rights-of-way, traffic and road conditions, land use patterns, building accessibility, and safety, among others. Walkability is an important concept in sustainable urban design.
One proposed definition for walkability is: "The extent to which the built environment is friendly to the presence of people living, shopping, visiting, enjoying or spending time in an area". Factors affecting walkability include, but are not limited to:
- Street connectivity
- Land use mix
- Residential density (residential units per area of residential use)
- Presence of trees and vegetation
- Frequency and variety of buildings
- Entrances and other sensations along street frontages
- Transparency, which includes amount of glass in windows and doors, orientation and proximity of homes, and buildings to watch over the street
- Plenty of places to go to near the majority of homes
- Placemaking, such as street designs that work for people, not just cars
- Retail floor area ratio 
Major infrastructural factors include access to mass transit, presence and quality of footpaths, buffers to moving traffic (planter strips, on-street parking or bike lanes) and pedestrian crossings, aesthetics, nearby local destinations, air quality, shade or sun in appropriate seasons, street furniture, traffic volume and speed. and wind conditions.
Walkability is also examined based on the surrounding built environment. Reid Ewing and Robert Cervero's five D's of the built environment, density, diversity, design, destination accessibility, and distance to transit, heavily influence an area's walkability. Combinations of these factors influence an individual's decision to walk.
Before cars were mass-produced, walking was the main form of transportation. Pedestrianism was the only way to get from place to place for much of human history. In the 1930s, economic growth led to increased automobile manufacturing. Cars were also becoming more affordable, leading to the rise of the automobile during World War II. Recently, the detrimental effects of automobile emissions have led to public concern over pollution. Environmentally friendly alternatives, like improved public transportation and walking infrastructure, have become more serious elements that planners and policymakers are paying attention to.
Walkability indices have been found to correlate with both Body Mass Index (BMI) and physical activity of local populations. Physical activity can prevent chronic diseases, such as cardiovascular disease, diabetes, hypertension, obesity, depression, and osteoporosis. The World Cancer Research Fund and American Institute for Cancer Research released a report that new developments should be designed to encourage walking, on the grounds that walking contributes to a reduction of cancer.
A further justification for walkability is founded upon evolutionary and philosophical grounds, contending that gait has been vital to the cerebral development in humans. After millennia of human development firmly based upon gait, the twentieth century automotive and automated metropolis has separated walking from thinking, and in this sense it has become an agent of regression rather than human progress. Walkability is offered as a critical component in contemporary urban design considerations, with implications far beyond the scope of current concerns.
Due to discrepancies between residents' health in inner city neighborhoods and suburban neighborhoods with similar walkability measures, it has been suggested that further research is needed to find additional built environment factors to be included in walkability indices.
One of most important benefits of walkability is the decrease of the automobile footprint in the community. Carbon emissions can be reduced if more people choose to walk rather than drive or use public transportation. The benefits of less emissions include improved health conditions and quality of life, less smog, and less of a contribution to global climate change.
Walkability has also been found to have many economic benefits, including accessibility, cost savings both to individuals and to the public, increased efficiency of land use, increased livability, economic benefits from improved public health, and economic development, among others. The benefits of walkability are best guaranteed if the entire system of public corridors is walkable - not limited to certain specialized routes. More sidewalks and increased walkability can promote tourism and increase property value.
In recent years, the demand for housing in a walkable urban context has increased. The term "Missing Middle Housing" as coined by Daniel Parolek of Opticos Design, Inc., refers to multi-unit housing types (such as duplexes, fourplexes, bungalow courts, and mansion apartments not bigger than a large house), which are integrated throughout most walkable Pre-1940s neighborhoods, but became much less common after World War II, hence the term "missing." These housing types are often integrated into blocks with primarily single-family homes, to provide diverse housing choices and generate enough density to support transit and locally-serving commercial amenities.
Auto-focused street design diminish walking and needed "eyes on the street" provided by the steady presence of people in an area. Walkability increases social interaction, mixing of populations, average number of friends and associates where people live, reduced crime (with more people walking and watching over neighborhoods, open space and main streets), increased sense of pride, and increased volunteerism.
Socioeconomic factors contribute to willingness to choose walking over driving. Income, age, race, ethnicity, education, household status, and having children in a household all influence walking travel.
Many communities have embraced pedestrian mobility as an alternative to older building practices that favor automobiles. Reasons for this shift include a belief that dependency on automobiles is ecologically unsustainable. Automobile-oriented environments engender dangerous conditions to both motorists and pedestrians, and are generally bereft of aesthetics 
There are several ways to make a community more walkable:
- Sidewalks can be implemented where there are "sidewalk gaps", with priority to areas where walking is encouraged, such as around schools or transit stations. Campaigns such as Atlanta, Georgia's safe routes to transit are providing safer access to transit stops for pedestrians. When implementing new sidewalks, there are several aspects to consider such as sidewalk width. The Americans with Disabilities Act (ADA) requires that sidewalks be at least five feet in width.
- Moving obstructions, like sign posts and utility poles, can increase the walkable width of the sidewalk. Quality maintenance and proper lighting of sidewalks reduces obstructions, improves safety, and encourages walking.
- Buffers, areas of grass between the street and the sidewalk, also make sidewalks safer. Vegetation from buffers absorbs the carbon dioxide from automobile emissions and assists with water drainage.
- Improving crosswalk safety also increases walkability. Curb extensions decrease the radii of the corners of the curb at intersections, calm traffic and decrease the distance pedestrians have to cross. On streets with parking, curb extensions allow pedestrians to see oncoming traffic better where they otherwise would be forced to walk into the street to see past parked cars. Striped crosswalks, or zebra crossings, also provide safer crossings because they provide better visibility for both drivers and pedestrians.
- New infrastructure and pedestrian zones replace roads for better walkability. Cities undertake pedestrian projects for better traffic flow by closing automobile access and only allowing pedestrians to travel through. Projects such as the High Line and the 606 Trail increase walkability by connecting neighborhoods, using landscape architectural elements to create visually aesthetic green space, and allow for physical activity. Towns can also be modified to be pedestrian villages.
- Monitoring and improving safety in neighborhoods can make walking a more attractive option. Safety is a main concern among children when choosing how to get to and from school. Ensuring safer walking areas by keeping paths well-maintained and well-lit can encourage walkability.
One way of assessing and measuring walkability is to undertake a walking audit. An established and widely used walking audit tool is PERS (Pedestrian Environment Review System) which has been used extensively in the UK. A number of commercial walkability scores also exist:
- Walk Score is a walkability index based on the distance to amenities such as grocery stores, schools, parks, libraries, restaurants, and coffee shops. Walk Score's algorithm awards maximum points to amenities within 5 minutes' walk (.25 mi), and a decay function assigns points for amenities up to 30 minutes away. Scores are normalized from 0 to 100.
- Walkability is a customizable set of three walk rating indexes with an algorithm that considers factors including street type, intersection complexity, point-of-interest accessibility, population density, freeways and bodies of water. Add-on scores include other factors like crime, weather, or public transit, among others.
- Walkonomics is a web app that combines open data and crowdsourcing to rate and review the walkability of each street. As of 2011, Walkonomics claimed to have ratings for every street in England (over 600,000 streets) and New York City.
- RateMyStreet is a website that uses crowdsourcing, Google Maps and a five star rating system to allow users to rate the walkability of their local streets. Users can rate a street using eight different categories: Crossing the street, pavement/sidewalk width, trip hazards, wayfinding, safety from crime, road safety, cleanliness/attractiveness, and disabled peoples' access.
- Walkability App developed by Clean Air Asia allows users to rate the walkability of a street qualitatively through 9 parameters. The individual scores are converted to a total out of 100. The average of all the street scores in a city becomes the city score. The parameters assessed include modal conflict, disability infrastructure, perception of safety, availability of crossing points, and motorist behavior, among others.
A simple way to determine the walkability of a block, corridor or neighborhood is to count the number of people walking, lingering and engaging in optional activities within a space. This process is a vast improvement upon pedestrian level of service (LOS) indicators, recommended within the Highway Capacity Manual. However it may not translate well to non-Western locations where the idea of "optional" activities may be different. In any case, the diversity of people, and especially the presence of children, seniors and people with disabilities, denotes the quality, completeness and health of a walkable space.
A newly developing concept is the transit time map (sometimes called a transit shed map), which is a type of isochrone map. These are maps (often online and interactive) that display the areas of a metropolis which can be reached from a given starting point, in a given amount of travel time. Such maps are useful for evaluating how well-connected a given address is to other possible urban destinations, or conversely, how large a territory can quickly get to a given address. The calculation of transit time maps is computationally intensive, and considerable work is being done on more efficient algorithms for quickly producing such maps. To be useful, the production of a transit time map must take into consideration detailed transit schedules, service frequency, time of day, and day of week.
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- levelofservice.com, Walkability tools research and walking level of service calculator.
- Walkshed.org, an online walkability mapping application using personal preferences.
- Pedestrian Environment Review System (PERS)
- RateMyStreet Walkability crowdsourcing project
- Get Your Walk Score - A Walkability Score For Any Address