Exploiting the flexibility of modular buses in an urban transit system

Urban transit systems usually operate according to fixed-route and fixed-schedule schemes by employing fixed-capacity vehicles, despite the mobility demand is unevenly spread out in both space and time. Modular buses are an emerging technology in which modules of relatively small capacity can be dynamically docked together to form greater capacity buses and can, therefore, make the transit system capable of adapting the capacity to the actual mobility demand. A module can be shifted from one line to another at pre-defined intersections and can be relocated when empty, if beneficial. We call these two operations sharing and rebalancing, respectively. Given a transit network comprising multiple bus lines and a mobility demand, we present an integer linear program to determine an optimal assignment of modules to lines, so that the mobility demand is met with a minimum total number of modules. Computational experiments show that, by exploiting the flexibility of modular buses, the total capacity deployed can be reduced by 49% with respect to a conventional transit system, whereas the average occupancy ratio increases from 41.22% to 72.85%.