Usually, the Reserve Fleet, or Spare Fleet, of passenger urban buses, is based on indicators used in some international relevant companies and extrapolated for many others, almost as a dogma. However, it must be taken into consideration pragmatic variables intrinsic to the buses namely their maintenance and in a more pragmatic approach, indexing their availability and by consequence the reserve fleet indexed to the maintenance policy used in each company.

The paper discusses these subjects and presents a global model that integrates the maintenance planning policy, based on a condition monitoring model, maintenance Key Maintenance Indicators (KPI), and an economic life cycle model.

The paper presents some results based both in theoretical considerations and also in real data from an urban fleet of a European Country.