A time B time vehicle half interval average wait Figure 1: A. Equal headways lead to shorter passenger waiting times at stations. On average, the waiting time at stations is half the intervehicle interval. B. With unequal headways, passengers also are expected to wait half the current intervehicle interval, but there is a higher probability of passenger arrival within longer intervals, leading to higher average waiting times [57]. Even when an equal headway configuration is desired, this is unstable, as explained in Figure 2. It is like an inverted pendulum, where any perturbation kicks the system off balance and brings the pendulum down. In a similar way, public transportation systems “prefer” to have unequal headways, as small delays amplify with a positive feedback, leading to the collapse of the system. Much of public transportation engineering for the past fifty years has dealt with trying to force transportation systems into maintaining an equal headway configuration [126]. In this context, a self-organizing method was developed with the aim of not only main- taining equal headways, but also to recover from unequal headway configurations. Following the inverted pendulum analogy, the goal was to build a system that would not only to prevent the pendulum from falling, but also to lift it up starting from a fallen position. Inspired by the adaptivity of ant communication [31], the method was tested and refined. One type of ant communication involves the secretion and sensing of pheromones. For example, if an ant finds a source of food, it will return to its nest with some food while leaving a pheromone trail. Other ants have a tendency to follow pheromone trails, proportional to the pheromone concentration. Thus, if more ants follow the pheromone trail and find the 19