01719nas a2200133   4500008004100000245009700041210006900138300001000207490000600217520126700223100002301490700002101513856005101534       2009                        eng d00aWhy does public transport not arrive on time? The pervasiveness of equal headway instability0 aWhy does public transport not arrive on time The pervasiveness o  ae72920 v43 aBackground 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. Methodology 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.1 aGershenson, Carlos1 aPineda, Luis, A.  uhttp://dx.doi.org/10.1371/journal.pone.0007292