Towards transfer synchronization of regularity-based bus operations with sequential hill-climbing

In this work we model and discuss how we can achieve coordination between different bus service lines. Key problem challenges are (a) the multiple conflicting priorities (on one hand the improvement of bus service regularity and on the other hand the reduction of passenger transfer waiting times) and (b) the computational complexity for re-scheduling the dispatching times of bus trips for meeting the conflicting priorities. Initially, a model for reducing the waiting times at bus transfer stations while also improving the operations of regularity-based bus services subject to operational constraints is introduced. Conflicting priorities are handled with the introduction of weight factors that allow bus operators to decide the trade-off between improvement of regularity-based operations and reduction of passenger waiting times at transfer stations. After that, an exterior point penalty function is introduced for handling operational constraints and a sequential hill-climbing search strategy is applied for converging to an approximate optimal solution. For our case study, we utilize general transit feed specification data from two regularity-based bus services in central Stockholm that intersect in five transfer stations. Experimental tests showcase a 13% potential waiting time improvement at transfer stations while sacrificing only 2.8% of service regularity and satisfying all operational constraints.