It seems that crowds behave in ways that can sometimes be predicted by physics.
Today’s invention is an overhead panel for walkways which consists of a diffusing screen behind which an array of green and red leds is located.
Each led unit is connected to a motion sensor which can detect coarsely the direction of movement of someone walking (or running) beneath.
In order to smooth the passage of a crowd moving both ways in the walkway, each person looks at the colour over their own head and then walks towards a patch of that colour on the ceiling.
This tends to coalesce individuals into a small number of streams (eg 2) which pass each other with less interruption.