**9.2 Residential: middle density and the intermediate housing**

There seems to be a conflict between epidemiologic studies that suggest a lower people density and the environmental approach that recommends the increasing of the built density. The urban sprawl is considered to increase pollution, to cause the loss of a sense of community [73], global warming [74], higher transportation costs and create health effects due to the dependence on automobiles [75]. It is addressed by professional organizations such as Architects' Council of Europe, the American Institute of Architects and the American Planning Association, by agencies such as European Environment Agency or by national legislation, such as the French law for Solidarity and Urban Renewal.

On the other hand, lowering the people density is not only implied by studies carried over time that correlate population density and pandemics but also the public preference. Pre-pandemic surveys showed that 76% of French [76] and 80% of US Americans [77] would choose to live in single-family houses. The COVID-19 pandemic increased this desire. Teleworking and the reduced access to shops, "led to a reduced demand for housing in neighborhoods with high population density", trend which strengthen after the market recovery in June 2020 [78].

**The solution to reconcile the dense city environmental paradigm with the low density of population suggested by epidemiologic studies can only find the answer in architecture and urbanism**. For most epidemiological approaches, people density is a figure in a quantitative approach while for architecture and urbanism there is also a shape-related morphological and typological building approach. Urban approach also considers different densities, such as population density (related to inhabitants' number), residential density (related to number of housings) or built density (related to gross floor area). Moreover, the same people density can be achieved with different urban typologies, such as parallel buildings, courtyard or scattered. Architectural approach also takes into account building morphology. The same people density can be achieved under different morphologies, such as detached houses, row houses or blocks. Therefore, addressing population density as a figure is not enough for analyzing the complexity of the built environment.

A more detailed approach should also be based on studies carried over the virus transmission in the interior spaces. Small, confined and poorly ventilated spaces, such as stairs or elevators, must be carefully planned as they are the most susceptible for aerosol contamination [79].

Medium density environments are the mostly supposed to reach this goal. Both New Urbanism and Urban village movements promote medium density housing. There are urban and architectural approaches that stay in between the single family detached house and the block paradigm. The French Intermediate Housing concept addresses buildings with more than one superposed apartments and with private access to each apartments. The definition appears in a French 1973 decree: the social intermediate housing (*habitat social intermédiaire*) is supposed to have a private access, a private exterior space of one quarter of the apartment surface and a height of no more than three floors. The organization led to densities of 80 to 100 dwellings per hectare for intermediate housing compared to the 10–50 dwellings per hectare for dense single-family houses [80].

#### **9.3 Public spaces: the key for the social interaction**

One of the problems the COVID-19 pandemic created was the social disruption. The public space was put under scrutiny [81]. In this matter, exterior public spaces

could play a key role. The COVID-19 droplets transmission occurs up to 6 feet (2 meters). According to Edward T. Hall's proxemics theories, the social distance far phase is in between 7 and 12 ft. (2.1–3.7 m) and the public distance is in between 12 and 25 ft. (3.7–7.6 m) for the close phase and more than 25 ft. (7.6 m) for the far phase. Therefore, far social and public contacts could be achieved in exterior spaces without transmission risks.

According to Jan Gehl's theories, social contacts in public spaces are among the most important. They have the characteristic of being spontaneous because people interact as a result of necessary or optional activities. The space in between the buildings is ideal for conversation, greetings, children playing: "life between buildings as dimension of architecture, urban design and city planning to be carefully treated [82]".

#### **9.4 Green areas: a perennial goal**

As recent scientific studies show, green areas can improve the response to pandemics. They were already present in the 1900s urban theories and they maintain their permanent importance.

#### **9.5 Working: downsizing and dispersion**

Architectural measures can be taken in the case of office buildings. Some approaches concern general building measures, such as air control by ventilation filtration and humidification. Other methods should lean on morphologic changes that consider access separation and office space distribution.

There is also question of the offices size and their urban distribution. During the COVID-19 pandemic, an Italian multicriterial research concluded that firm density, based on an over 250 employees firm index for each region, was positively associated with higher fatality rates [36].

The COVID-19 pandemic also accelerated the use of telecommuting (teleworking or working from home). In 2019, 5.5% of workers in the US already worked from home [83] and, in April 2020, already 20% of Americans were able to work from home and doing so [84]. Estimations from 2020 are that "37 percent of U.S. jobs that can plausibly be performed at home account for 46 percent of all wages [85]". Telecommuting has an indirect environment impact by reducing the greenhouse emissions, fuel and energy usage and network congestion [86, 87].

#### **9.6 Shopping: proximity and downscaling**

Apart air quality methods, different measures can be taken for shops. Reducing the size cold lead to a better ventilation and less potential contacts. Proximity shopping is also an environmental desideratum as it allows for less automobile transportation, lead to pedestrian cities, reduced pollution, less energy consumption and less environmental impacts. Recent study shows that "to achieve a balance between energy consumption, GHG [Greenhouse Gas] emissions and energy generation potential, a neighborhood should contain an optimal ratio of commercial to residential buildings of about 0.25 [88]."

The proximity and downscaling decision have long term social and environment motivations more than short term economic reasons. An example are hypermarkets, huge stores combing supermarkets to department stores. It is symptomatic how France, the country that first implemented hypermarkets with Carrefour, in 1963, prevented their implantation in cities ten years later, by the Royer law which regulated the creation of shops over 1500 m2 inside towns.

## **9.7 Transportation: walking, bicycling, shared mobility and robo-taxis**

Before the pandemic there was already very strong evidence of aerosol transmission over long distances [89]. Studies during 2020 showed substantial transmission in closed vehicles and suggest "future efforts at prevention and control must consider the potential for airborne spread of SARS-CoV-2, which is a highly transmissible pathogen in closed environments with air recirculation [90]". At the beginning of 2020, studies drew a warning about public transportation showing that, for New York City, the subway system was the major disseminator of COVID-19 [91].

To keep the present transportation system there could be applied methods that reduce the viral transmission. Airborne virus spread in public transport can be reduced by installing HEPA filters and surface disinfection can be done by UV disinfection.

There is also question of changing the current transportation paradigm. Changes that may reduce the virus transmission in the transportation system already begun before the COVID-19 pandemic. Cities designed at the scale of walking or bicycle distances were proposed by the 1900s Garden City movement, the 1970s Intermediate Housing or 1980s New Urbanism and Urban Village movements.

Mobility sharing with bicycles can increase the efficiency of an urban public transport network [92] and has health benefits [93]. Starting with the white bicycle and white path proposed by the Provo movement in Amsterdam, in 1965, the Vélib' in Paris, launched in 2007 and reached the Chinese bike sharing system where the two largest operators, Ofo, launched in 2014, and Mobilke 2015, totalize over 50 million orders per day [94]. Electric car sharing, on which UV disinfection could be applied, could be a pandemic and environmental solution too. It has a positive environmental approach by "reducing 29% of CO2 emissions and increasing 36% electric vehicle adoption, when compared to the business-as-usual scenario [95]". Along with UV disinfection, robo-taxis (robocabs, self-driving taxis or driverless taxis) could be used. Experiment in Beijing with electric robo-taxis showed a good impact in lower energy consumption, zero tailpipe emissions, traffic decongestion and reduced health risks [96] while simulation in Milan "propose that introducing a robo-taxi fleet of 9500 vehicles, centered around mid-size 6 seaters, can solve traffic congestion and emission problems in Milan [97]".

From the larger urban point of view, transportation is influenced not only by the means of transport but also by the overall cities' organization.
