Nowadays fleet management is playing a fundamental role in private as well as in public organizations. Particularly important is considered the role of fleet management when decision makers have to decide whether to undertake strategic policies about fleet renewal or strategic policies aimed at containing investment costs through, for example, a better maintenance management. However, the adoption of such strategies may produce several effects in short and long term on business outcomes and may also affect other key performance drivers. This paper explores how the System Dynamics (SD) methodology can support managers for the effectiveness of decision-making process about fleet management, advising on a systemic perspective for analysing the main effects resulting by the adoption of different strategic policies. Moreover, a case study on how SD has been deployed to provide a fleet management decision support system for the managers of a public-owned company operating in the field of waste management services is provided. Finally, scenario analysis is presented and discussed.