This is the case with health and education services, particularly in those areas heavily dependent on intangible investments (such as in R&D and skills), which may not require large sunk costs but do require ongoing investments to maintain and improve the services provided. However, externalities persist, and other market failures complicate their delivery. This is particularly the case where infrastructure provision is closely linked to networks. These characteristics are found mainly in the energy, water, public transport and telecommunications sectors, although variations exist within sectors, across countries and over time.2 These are, moreover, the sectors that have traditionally been seen as having a more direct impact on economic growth and structural transformation.