The planning of traction units and drivers is a crucial strategic and tactical planning problem for railway companies. Due to the complexity of the individual problems, large railway undertakings typically solve these problems in a sequential manner, i.e., they first generate circulation plans and then use them to generate shift plans. As a consequence, the achievable quality of the shift plans depends on the operational efficiency of the circulation plan, and information dependencies between the two planning steps cannot be exploited. This paper presents different types of integrated circulation and shift planning. An investigation of the inherent challenges and benefits of an integrated planning approach is presented, initial approaches for data structures and algorithms are introduced, and first results are shown.