Car dependency is a pattern in urban planning that occurs when infrastructure favors automobiles over other modes of transport, such as public transport, bicycles, and walking. Car dependency is associated with higher transport pollution than transport systems that treat all transportation modes equally.

Car infrastructure is often paid for by governments from general taxes rather than gasoline taxes or mandated by governments. For instance, many cities have minimum parking requirements for new housing, which in practice requires developers to "subsidize" drivers. In some places, bicycles and rickshaws are banned from using road space, and pedestrian use of road space has been criminalized in many jurisdictions (see jaywalking) since the early 20th century. The road lobby plays an important role in maintaining car dependency, arguing that car infrastructure is good for economic growth.

In many modern cities, automobiles are convenient and sometimes necessary to move easily. When it comes to automobile use, there is a spiraling effect where traffic congestion produces the 'demand' for more and bigger roads and the removal of 'impediments' to traffic flow. Examples of such impediments can for instance be pedestrians, cyclists, signalized crossings, traffic lights, various forms of street-based public transit such as buses and trams, or even houses, parks and recreational arenas.

These measures make automobile use more advantageous at the expense of other modes of transport, inducing greater traffic volumes. Additionally, the urban design of cities adjusts to the needs of automobiles in terms of movement and space. Buildings are replaced by parking lots. Open-air shopping streets are replaced by enclosed shopping malls. Walk-in banks and fast-food stores are replaced by drive-in versions of themselves that are inconveniently located for pedestrians. Town centers with a mixture of commercial, retail, and entertainment functions are replaced by single-function business parks, 'category-killer' retail boxes, and 'multiplex' entertainment complexes, each surrounded by large tracts of parking.

These kinds of environments require automobiles to access them, thus inducing even more traffic onto the increased road space. This results in congestion, and the cycle above continues. Roads get ever bigger, consuming ever greater tracts of land previously used for housing, manufacturing, and other socially and economically useful purposes. Public transit becomes less viable and socially stigmatized, eventually becoming a minority form of transportation. People's choices and freedoms to live functional lives without the use of the car are greatly reduced. Such cities are automobile-dependent.

Automobile dependency is seen primarily as an issue of environmental sustainability due to the consumption of non-renewable resources and the production of greenhouse gases responsible for global warming. It is also an issue of social and cultural sustainability. Like gated communities, the private automobile produces physical separation between people and reduces the opportunities for unstructured social encounters that is a significant aspect of social capital formation and maintenance in urban environments.

As automobile use rose drastically in the 1910s, American road administrators favored building roads to accommodate traffic. Administrators and engineers in the interwar period spent their resources making small adjustments to accommodate traffic such as widening lanes and adding parking spaces, as opposed to larger projects that would change the built environment altogether. American cities began to tear out tram systems in the 1920s. Car dependency itself saw its formation around the Second World War, when urban infrastructure began to be built exclusively around the car. The resultant economic and built environment restructuring allowed wide adoption of automobile use. In the United States, the expansive manufacturing infrastructure, increase in consumerism, and the establishment of the Interstate Highway System set forth the conditions for car dependence in communities. In 1956, the Highway Trust Fund was established in America, reinvesting gasoline taxes back into car-based infrastructure.

In 1916 the first zoning ordinance was introduced in New York City, the 1916 Zoning Resolution. Zoning was created as a means of organizing specific land uses in a city so as to avoid potentially harmful adjacencies like heavy manufacturing and residential districts, which were common in large urban areas in the 19th and early 20th centuries. Zoning code also determines the permitted residential building types and densities in specific areas of a city by defining some areas as single-family zoning, and other areas where multi-family residential is allowed. The overall effect of zoning in the last century has been to create areas of the city with similar land use patterns in cities that had previously been a mix of heterogenous residential and business uses. The problem is particularly severe right outside of cities, in suburban areas located around the periphery of a city where strict zoning codes do not allow any residential types other than single family detached housing. Strict zoning codes that result in a heavily segregated built environment between residential and commercial land uses contribute to car dependency by making it nearly impossible to access all one's given needs, such as housing, work, school and recreation without the use of a car. One key solution to the spatial problems caused by zoning would be a robust public transportation network. There is also currently a movement to amend older zoning ordinances to create more mixed-use zones in cities that combine residential and commercial land uses within the same building or within walking distance to create the so-called 15-minute city.