After several more stops, the second bus inevitably catches up with the first. Once one bus catches up with the other, the two buses act as if they were a single bus. If the route is a long one, a third bus could eventually catch up with the first two. Bus transport in Cuernavaca, Mexico, operates differently. Although passengers wait at bus stops along specified routes, there are no schedules.
Drivers own their buses and compete for passengers.
To pick up as many passengers as possible, they constantly slow down or speed up, depending on the number of other buses in the vicinity. Indeed, drivers even employ people to stand at checkpoints along a route and tell them when the last bus left a particular area so they can adjust their speed accordingly, staying far enough behind the preceding bus without letting the following bus catch up. Despite the apparently chaotic transport system, there is a sort of statistical order in the collective behavior of the vehicles. Physicists Petr Seba and Milan Krbalek of the Czech Academy of Sciences have found that Cuernavaca buses move about like randomly interacting subatomic particles. This activity can be described in terms of mathematical expressions called random matrices, which were originally used to describe the quantum energy levels of large atoms or heavy atomic nuclei.