The way that people walk in public is a source of seemingly infinite frustration. Walking too slow, stepping on someone's heels, shouldering past without so much as a sorry; it feels like there's always somebody out there who has zero conception of personal space or even the most basic social courtesies.
But for all our complaining, when most of us march out the front door, we generally try and avoid getting in the way of others. And when all is said and done, collisions between strangers on the sidewalk are quite rare. At worst, it's usually just an awkward shuffle.
Analysing pedestrian movements in a Dutch train station, physicists have now figured out what keeps us from crashing into our fellow travellers more often.
The answer is space - at least 75 centimetres (29.5 inches) of it to be exact.
According to the study, that's what's needed to stop you annoyingly bumping into other pedestrians (close walkers, take note).
Using overhead sensors kind of like the ones on a Wii console, the researchers analysed the movements of more than 5 million pedestrians at the Eindhoven station in the Netherlands over the course of six months. The spot selected was a small subsection of a corridor with only two lanes of traffic: one way, or the other.
The vast majority of the time, the people who passed through this area liked to keep an average distance of at least 75 centimetres (29.5 inches).
And even when they got a little too close, they unconsciously changing their path to avoid others.
The team identified that out of all those 5 million pedestrians, 9,000 pairs of star-crossed travellers (just 0.18 percent) were on course to bump into each other. But most avoided the incident.
"About 40 pairs of these actually bumped into each other," says co-author Alessandro Corbetta, a researchers in pedestrian dynamics at Eindhoven University of Technology.
"The remaining pairs adapted their walkways until they were at least 140 centimetres apart and were therefore able to prevent a collision."
This means that of all the movements observed in this particular corridor of the Eindhoven train station, only 0.000016 percent actually resulted in brushing up against someone else's personal bubble.
The findings have led the authors to conclude that "[w]hile in motion, pedestrians continuously adapt their walking paths trying to preserve mutual comfort distances and to avoid collisions."
The next step was using all of that data to develop and train a computer model that could predict pedestrian movements in a crowded space.
The authors hope that the resulting model will not only improve urban planning and civil facilities, but also add to our understanding of fluid dynamics even further.
Because while most of us think of water when we hear the word "fluid", when physicists talk about fluidity their imaginations run wild and they consider everything from flocks of birds to fishes in a shoal, or even, maybe, pedestrians in a crowd.
"I always try to go a step further in the complexity of pedestrian movements," says co-author Federico Toschi, an expert in applied physics and mathematics at Eindhoven University.
"I dream of eventually understanding the dynamics of a whole dense crowd."
This study has been published in Physical Review E.