In a recent email to an old friend I described my movements through the world of social distancing:
I continue to go out twice a day for runs and walks. It’s started to feel more like a kind of game, keeping track of who else is out there and altering my trajectory to maintain safe distance. Bicycles coming up from behind are the biggest challenge, so I’ve adjusted my habits to looking behind me every 30 seconds or so. I’ve also taken to wearing my Biohazard t-shirt on afternoon runs — it might not serve as fair warning but it seems to cloak me in a kind of absurdist protective psychological bubble. The first day I wore it a passing motorist rolled down his window and shouted NICE SHIRT at me — that’s the spirit.
In reply my friend linked me to a NYT article written by a dancer, who describes the collective maneuvers required to sustain social distancing in public places as a kind of choreography:
In this time of confinement, we have been given one immeasurable gift — the freedom to go outside. In exchange, we must abide by a simple rule: Stay six feet away from others. As choreographic intentions go, that’s not remotely vague. Yet during my runs and walks in Brooklyn over the past few days, I’ve noticed that six feet doesn’t mean the same thing to everybody.
Spatial awareness, like coordination, isn’t a given. Watching the choices people make when they move in public, much less in this time of social distancing, can be shocking, from the much-bemoaned tourist who comes to a grinding halt in Times Square to the woman with a yoga mat knocking people aside to get her spot on the floor. (It’s OK; she’ll still feel good about bowing her head and saying namaste.)
The six-feet-away rule is simple, but it’s a proxy. We’re not trying to dance around one another; we’re trying to dance around the virus — an invisible partner.
A 2007 study measured the distances that breath droplets can travel before evaporating when expelled by breathing, sneezing, and coughing. Ordinary breath travels at a rate of 1 meter per second, with droplets evaporating within less than 1 meter distance from the breather. Coughing doubles the droplet spray distance, so maintaining a social isolation zone of 2 meters (61⁄2 feet) seems adequate for coronavirus.
But what if the breather is walking? At 3 MPH, a walker travels 1.3 meters per second. Add walking speed to breath speed and the walker’s breath droplet precipitation zone extends to 2 meters — still good, as long as nobody coughs or sneezes. What if another walker is walking toward me? Add that person’s 2 meters to mine = 4 meter distancing seems okay. What about a runner? At an average running speed of 6MPH or 2.7 meters/second, the droplet trail extends to around 3.5 meters. A bicyclist traveling at 15MPH generates a breathing droplet trail of around 7.5 meters.
These calcs support the intuitive sense that safe distance is correlated with speed — pretty much like anticipating safe braking distance while driving at different speeds. It’s the game played at level 2, demanding more intricate choreography than the simple 6-foot rule of level 1.
On the trails it’s the bicyclists who make the choreography most difficult, dragging their spray of breath droplets in their wake while coming up at speed from behind. But the walkers tend to stretch themselves in clumps across the entire width of the trail. So I’ve taken to walking and running along the sides of the roads. Drivers of cars are pretty much keeping their breath to themselves. And while cars too exhale noxious fumes, these days it’s a matter of picking your poison. And of course being bumped by a fellow pedestrian isn’t quite the same level of hazard as being bumped by a car.
It’s 7am — time to dance my way through the viral chorus line…