You are walking along a busy pavement in Paris and another pedestrian is approaching from the opposite direction. Moving to one side is necessary to avoid the collision…but which way do you go?

According to an article in The Economist, if you are French the answer is almost certainly to the right. If you are Chinese, however, it is probably to the left. There is normally no instruction for the choice of a specific direction except if you are South Korean. In South Korea, there is a campaign to get people to walk on the right.

Mehdi Moussaid of the Max Planck Institute in Berlin and Dirk Helbing of ETH Zurich, a technology-focused university, are at the cutting edge of a youngish field – understanding and modelling how pedestrians behave. Knowing about the propensity of different nationalities to step in different directions could help make crowded events safer.

In 1995, Mr. Helbing and Peter Molnar, both physicists, analysed pedestrian movement using a computer model based on the way that particles in fluids and gases behave. The model assumed that people are attracted by some things, such as the destination they are heading for, and repelled by others, such as another pedestrian in their path. It proved its worth by predicting several self-organising effects among crowds that are visible in real life.