  Cities all around the world struggle with urban air quality due to
transportation related emissions. In public transport networks, replacing
internal combustion engine buses by electric buses provides an opportunity to
improve air quality. Hence, many bus network operators currently ask for an
optimal transformation plan to integrate battery electric buses into their
fleet. Ideally, this plan also considers the installation of necessary charging
infrastructure to ensure a fleet's operational feasibility. Against this
background, we introduce an integrated modeling approach to determine a
cost-optimal, long-term, multi-period transformation plan for integrating
battery electric buses into urban bus networks. Our model connects central
strategic and operational decisions. We minimize total cost of ownership and
analyze potential reductions of nitrogen oxide emissions. Our results base on a
case study of a real-world bus network and show that a comprehensive
integration of battery electric buses is feasible and economically beneficial.
By analyzing the impact of battery capacities and charging power on the optimal
fleet transformation, we show that medium-power charging facilities combined
with medium-capacity batteries are superior to networks with low-power or
high-power charging facilities.
