The advent of automobility unlocked dimensions of transportation previously unavailable—a degree of access, mobility, freedom from scheduled and fixed route systems, and speed that “subordinated” other available modes [1, 2]. There are an estimated 2.2 billion registered motor vehicles (including motorcycles) globally, a number that is expected to increase in the years to come and double by 2040 . China (290 million), the USA (280 million), and India (210 million) account for the highest number of registered vehicles in the world . Developing nations—particularly India and China—are expected to see the largest increase in car ownership over the coming decades compared to other nations . In 2019, however, global motor vehicle sales totaled 51.4 million, down from 55 million sold in 2018 and the lowest since 2011 .
Cars became ingrained in modern society throughout the twentieth century for multiple reasons. First, the Model T car produced by the Ford Motor Company was one of the early products to optimize the benefits of industrialization, technological and design innovations, and mass production, which allowed Ford to reduce manufacturing costs and provide the first widely affordable mode of motorized transportation (The Model T) .
Second, the automotive industry provided an important source of jobs, peaking in the USA in the early twenty-first century . This success exemplified the economic potential of the automotive industry and countries such as France, Germany, Italy, Japan, and South Korea also expanded their economies through the automotive industry . Despite early successes, the adverse impacts of the automotive industry are exemplified through the history of Detroit, USA, which underwent a historic population increase provoked by the economic ascent of automotive manufacturing in the early twentieth century. This was followed by decades of decline as factories (and jobs) vacated the city and devastated the local economy and was apparent in other states of the American Midwest [7, 9]. Similar processes of decline and automotive de-industrialization have occurred in regions of Canada and the UK [10, 11]. Nearly 60% of car manufacturing in the U.K. was located in the West Midlands at the beginning of the 1970s, however, only 18% of car manufacturing still occurred in the region in 2008, corresponding with a 70-80% reduction in automotive jobs among certain manufacturers in the region . More recently, Oshawa, Canada was the wealthiest Canadian city for a decade due to large automotive manufacturing plants until a decline in the automotive industry eliminated over one-third of automotive jobs and diminished the economic well-being of the population as a whole .
Third, as car ownership proliferated, cars have become central to the way we build cities and use land, interact with the built environment, satisfy our travel needs, and much more . The convenience as represented in reduced travel time, increased comfort, improved accessibility, and ease of mobility compared to other modes in the early twentieth century made them attractive options. The dependence on cars manifested itself in the urban built environment in the form of low-density sprawl, single mixed-use developments, extensive road networks, and enormous parking lots. In many cities, zoning regulations mandate a minimum provision of parking spaces to improve automobile access to amenities. Parking minimums, however, often overestimate the necessary volume of parking spaces which results in higher development costs due to the high cost of parking construction . The growth of cities and changing spatial distribution of populations as transportation modes evolved from walking, to streetcars, to automobiles clearly express the impact of the car on urban form . Further, the invasion of cars into public space due to car-oriented development has revealed the spatial inefficiency of cars and their adverse impact on urban lifestyles, raising questions about the “fairness” of how road space, and therefore urban space, is allocated [15,16,17]. An “ego-enhancing medium” , cars also became symbols of status and privilege, further deepening the significance of car ownership in urban societies .
Economic assessments have been used in the past to estimate the relative cost of various transportation modes. Cars are estimated to produce external costs that society at-large must bear, most notably: vehicle crashes, air pollution, time lost due to congestion, physical inactivity, and urban space consumption . Litman (2009) estimated the greatest cost reduction for the public could be achieved if car trips were replaced with walking and cycling, largely due to the health benefits of active travel . These findings are supported by other cost–benefit analyses that suggest car travel incurs a fiscal burden on societies whereas active travel modes produce cost-savings mainly through the health benefits of physical activity [20, 21].
Recent work has identified 14 pathways that link transportation and health, 11 of which are associated with negative health outcomes [22••]. These 11 pathways are: physical inactivity, air pollution, motor vehicle crashes, noise, heat, stress, community severance, social exclusion, greenhouse gases, contamination, and electromagnetic fields. Dependence on cars, and its impact on the built environment exacerbates the negative health outcomes associated with these 11 pathways. Three pathways—access, green space, and mobility independence—were identified as producing positive health outcomes. The adoption of car-free initiatives can reduce the health burden of cars (such as decreasing air pollution, road-traffic noise, and motor vehicle crashes) and expand opportunities for health-promoting transportation practices by encouraging non-motorized transportation modes and physical activity.
In 2019, an estimated 90% of the global urban population lived in areas where average fine particulate matter (PM2.5) concentrations exceeded the World Health Organization (WHO) air quality guidelines . Transportation-related air pollution (TRAP) can account for up to 53% of PM10 and 66% of PM2.5 concentrations in European cities, although the prevalence of TRAP depends on location-specific factors and some cities may not be characterized by high TRAP concentrations . The countries with the highest average annual transportation-related PM2.5 concentrations are located in Southeast Asia (where vehicle ownership is also anticipated to increase the most ), Southwestern Europe, and India . Transportation-related PM2.5 was estimated to cause 107,000 annual premature deaths in the USA  and 137,000 annual premature deaths in China . Anenberg et al. (2019) showed that transportation-related emissions increased levels of ozone and PM2.5 which were estimated to account for 385,000 premature deaths globally in 2015 .
Motor vehicle crashes are the leading cause of death globally among 5-29 years old and are responsible for 1.35 million premature deaths each year across the total population . The total burden of disease associated with transportation noise in Europe (including rail, road, and air traffic) is estimated to be comparable to that of second-hand smoke . Many cities around the world are characterized by inhospitable levels of traffic congestion—the average car commuter in the 10 most congested cities will roughly spend 162 hours in traffic annually , which is found to reduce social ties and opportunities for social interaction . The adoption of cars as the preferred travel mode has increased the amount of sedentary behavior individuals engage in . Traveling by car is the least active mode, followed in ascending order by public transportation, walking, and cycling . Car-oriented lifestyles can partly explain the growth of physical inactivity as one of the leading causes of premature death globally (5.3 million deaths in 2008). Cumulatively, physical inactivity, motor vehicle crashes, and TRAP account for over 7 million premature deaths globally, and this burden is only a snapshot of the real health burden as it does not account for other important risk factors such as traffic noise, contamination, stress and the health impacts of climate change.
The contribution of cars and road transportation to climate change is perhaps the gravest health risk. Greenhouse gases (GHGs) trap heat from solar radiation within the Earth’s atmosphere which contributes to the warming of Earth’s climate as more GHGs are emitted. Carbon dioxide (CO2) is the most common GHG, composing 76% of global GHG emissions . In the USA, transportation emits more CO2 (28%) than any other sector . Globally, transportation is responsible for 23% of all CO2 emissions . The Intergovernmental Panel on Climate Change estimates that global GHG emissions need to be reduced by 45% of 2010 volumes by 2030—before ultimately achieving carbon neutrality by 2050—to avoid a global warming of 1.5°C . Global warming is directly harmful to health through increased risk of heatwaves, droughts, natural disasters such as wildfires, floods, and storms, higher levels of ambient air pollution, adverse impacts on food systems and infectious disease vectors, and potential ecosystem collapse [37, 38]. Reducing the use of cars would limit urban GHG emissions, improve existing urban environmental conditions, and result in healthier behaviors among urban dwellers .
While directly limiting automobility would technically be the most desirable option, this meets a lot of resistance including from policy makers, car lobbies, and the population [40, 41]. In this light, so-called transition experiments are useful to let policy makers and urbanites experience the benefits of reductions in, or bans of, automobility in certain areas. Car-free days or events are planned efforts to temporarily limit or restrict private car use and prioritize movement by walking, cycling, and public transportation instead. Early on, car-free Sundays were held to limit oil consumption, such as in the Netherlands in 1939 and 1956 and in several countries during the oil crisis in 1973-4 . Since the beginning, automobility has been controversial , but especially since the 1970s, resistance against the negative effects of automobility has become more pronounced (such as the Dutch “stop the child murder” movement) . Initial adoption for car-free initiatives can also be traced to cities such as Bogotá, Colombia, Venice, Italy, and Zurich, Switzerland as early as the 1970s, eventually becoming more widely adopted in Europe during the 1990s and early 2000s . The movement to encourage non-motorized, active travel could be a useful strategy to reduce dependence on cars and produce environmental and public health benefits.
The scale of car-free days or events is highly variable. Some car-free activities occur once, others annually (World Car-free Day), while still others recur as frequently as once per week, and are strictly enforced and supported by local governments, with defined geographic bounds within cities (e.g., Ciclovía in Bogotá, Colombia). The rationale for car-free days or events vary from addressing environmental and climate change concerns , pursuing transportation equity , and visioning how alternative mobility can improve general quality of life (health, social cohesion, etc.) . The general underlying motivation of car-free days and events, however, is to prioritize alternative modes of transportation to the car.
Recently, stay-at-home and work-from-home orders prompted by the COVID-19 pandemic drastically reduced motor vehicle traffic and increased the demand for outdoor recreational space [49,50,51,52]. In response, some cities began closing streets off to cars to create more pedestrian and cyclist-friendly street environments that facilitate socially distanced recreation and exercise . The benefits of these temporary car-free initiatives have encouraged citizens to demand these spaces remain car-free as restrictions are lifted .
The goal of this paper is to review examples of car-free days and events from around the world. The review includes academic and gray literature that discuss the emergence of car-free days and events, and their public health implications. Car-free initiatives have become increasingly popular and this paper synthesizes key examples of such initiatives and distills their health impacts. We also briefly discuss barriers and facilitators to the implementation of car-free initiatives. While the review of health impacts pertains to car-free days and events, the discussion of barriers and facilitators is broadened to include car-free city initiatives because the body of literature discussing barriers and facilitators largely focuses on car-free cities, not days and events.