The evidence so far indicates that the virus is spread from person to person through small respiratory droplets.
When a person sneezes, coughs or even exhales, he or she is emitting small droplets ―often too small to see with the naked eye―, that can carry the virus. The receiving persons can be infected by inhaling these droplets, or by getting these droplets on their hands and then touching their face.
In this way, social distancing ―recommended by countries world-wide, sometimes by law―, can offer protection (reduction in risk of infection) to susceptible individuals, and/or containment (reduction in risk of onward transmission) to infected individuals. The most common social distancing recommended by governments is a safety strip of 1 and 1.5 meters, a space that seems effective when the person is standing or there is no wind outside.
However, a recent study from the universities of KU Leuven (Belgium) and TU Eindhoven (Netherlands) has concluded that the safety distance should be greater when going for a walk, running or cycling.
A social distance of about 1 and 1.5 m between individuals is considered effective because it is expected that most of the droplets indeed fall down and reach the floor and/or evaporate before having traveled a distance of 1 and 2 m. However, this social distance has been defined for persons that are standing still. It does not take into account the potential aerodynamic effects introduced by person movement, such as walking fast, running and cycling ―when someone during a run breathes, sneezes or coughs, those particles stay behind in the air, and the person running behind in the so-called slip-stream goes through this cloud of droplets―.
This aerodynamics study investigates whether a first person moving nearby a second person at 1.5 m distance or beyond could cause droplet transfer to this second person.
The results indicate that the largest exposure of the trailing person to droplets of the leading person for walking and running is obtained when this trailing person is in line behind the leading person, i.e. positioned in the slipstream. Besides, the exposure increases as the distance between leading and trailing person decreases.
This suggests that avoiding substantial droplet exposure in the conditions of this study and in a way equivalent to the 1.5 m for people standing still can be achieved by one of two actions: either by avoiding to walk or run in the slipstream of the leading person and keeping the 1.5 m distance in staggered or side by side arrangement, or by keeping larger social distances, where the distances increase with the walking or running speed.
Out of the simulations, it appears that social distancing plays less of a role for 2 people in a low wind environment when running/walking next to each other. The droplets land behind the duo. When people are positioned diagonally behind each other the risk is also smaller to catch the droplets of the lead runner. Nevertheless, the risk of contamination is the biggest when people are just behind each other, in each other’s slipstream.
On the basis of these results the advice is that for walking the distance of people moving in the same direction in one line should be at least 4–5 meter, for running and slow biking it should be 10 meters and for hard biking at least 20 meters. Also, when passing someone it is advised to already be in different lane at a considerable distance e.g. 20 meters for biking.
Link to the paper: http://www.urbanphysics.net/COVID19_Aero_Paper.pdf
Editorial Disclaimer: information published during the 2020 COVID-19 pandemic may be updated frequently to reflect the dynamic nature of current understanding.