Sustainable and convenient: Bi-modal public transit systems outperforming the private car

Mobility is an indispensable part of modern human societies, but the dominance of motorized individual traffic (MIV, i.e., the private car) leads to a prohibitive waste of energy as well as other resources. Public transportation with line services, such as light rail, can pool many more passengers, thereby saving resources, but often is less convenient (longer transit times). Door-to-door shuttle services, on the other hand, are convenient but have a limited pooling efficiency due to detours scaling with shuttle occupancy. Combining line services with a fleet of shared shuttles in an integrated so-called bi-modal system may provide on-demand door-to-door service at a service level superior to current public transport with significantly less resource consumption than MIV. Here we introduce a generic model of bi-modal public transit and characterize its critical parameters of operation. We identify the conflicting objectives for optimization, i.e., user convenience and energy consumption, and evaluate the system’s performance in terms of Pareto fronts. By means of simulation and analytical theory, we find that energy consumption can be as low as 20% of MIV, at line service densities typically found in real settings. Road traffic can be reduced to less than 10% of MIV. Surprisingly, we find favorable performance not only in urban, but also in rural settings. We thereby provide a possible answer to the pressing question of designing sustainable future mobility solutions.