Modeling Modular Vehicle-Based Bus Systems Considering Coupling Failure Risk

Abstract A modular vehicle (MV) is a modern type of bus capable of coupling and detaching in motion. When applied to public transit services, MVs enable stop-less operation, eliminating passenger dwell time at intermediate stations and significantly enhancing the attractiveness of public transit service. However, unpredictable traffic conditions introduce the risk of in-motion coupling failure. If in-motion coupling fails while MVs are passing a given station, the MVs to be coupled must stop together at the next station to ensure that all passengers can disembark as planned. This additional stop may therefore affect passenger experience and vehicle operating cost, influencing the applicability of MVs in public transit services. In this paper, we consider MVs operating on a single cyclical route and formulate a system of linear equations to determine the probability that MVs stop at each station, given the coupling failure probability between stations. This allows us to estimate vehicle dwell times at intermediate stations and further evaluate the realized passenger travel cost and vehicle operating costs. The theoretical analysis provides a sufficient condition under which the MV system is cost-efficient under homogeneous coupling failure probabilities and shows that the MV advantage depends on the origin–destination distribution, station density, and coupling failure probability. Simulations under uncertain travel time support the theoretical results and indicate that this condition is conservative under mild operating conditions. The experiments further show that heterogeneous coupling failure probabilities have little effect on MV system performance when the mean failure probability is fixed.