Why does public transport not arrive on time? The pervasiveness of equal headway instability.
BACKGROUND
The equal headway instability phenomenon is pervasive in public transport systems. This instability is characterized by an aggregation of vehicles that causes inefficient service. While equal headway instability is common, it has not been studied independently of a particular scenario. However, the phenomenon is apparent in many transport systems and can be modeled and rectified in abstraction.


METHODS
We present a multi-agent simulation where a default method with no restrictions always leads to unstable headways. We discuss two methods that attempt to achieve equal headways, called minimum and maximum. Since one parameter of the methods depends on the passenger density, adaptive versions--where the relevant parameter is adjusted automatically--are also put forward. Our results show that the adaptive maximum method improves significantly over the default method. The model and simulation give insights of the interplay between transport design and passenger behavior. Finally, we provide technological and social suggestions for engineers and passengers to help achieve equal headways and thus reduce delays.


CONCLUSIONS
The equal headway instability phenomenon can be avoided with the suggested technological and social measures.
Gershenson
Carlos
C
Computer Sciences Department, Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Universidad Nacional Autónoma de México, Ciudad Universitaria, México D.F., México. cgg@unam.mx
Pineda
Luis A
LA
D000465:Algorithms; D001334:Automobile Driving / Q000523:psychology*; D003198:Computer Simulation; D004215:Distance Perception; D030141:Feedback, Psychological; D006801:Humans; D008962:Models, Theoretical; D013997:Time Factors; D014186:Transportation