In the context of development assistance, the basic idea of sustainability is that projects should be designed to produce a continuous flow of outputs, services, and outcomes over their economic lifetime. Historically, evidence on the sustainability of projects has been limited. But like other development agencies, ADB has become increasingly concerned with the sustainability of the activities it supports.
The objective of this special evaluation study is to assess ADB's achievements in the sustainability of its projects and programs, and ADB's approach to project sustainability. In a review of 491 ADB-assisted project completion reports between 2001 and 2009, 65% were rated most likely or likely to be sustainable; implying a "substantial task" after completion of enhancing the sustainability of the remaining 35% of the reviewed projects.
Among the study's findings was that effectiveness and efficiency do not guarantee the sustainability of project net benefits. It says: "There is still a substantial task of ensuring greater sustainability for projects rated effective and efficient." But at project completion, it is still possible to undertake a scenario analysis of key project features to identify where additional resources to enhance sustainability could best be implemented.
The study found that a key sustainability issue in the roads sector was an appropriate balance between investment for network expansion and the maintenance requirements for existing roads. The water supply and sanitation sector featured several constraints to sustainability, including lack of revenue-generating powers. The study recommends strengthening ADB's approach to identifying and mitigating risks to project sustainability during country and sector assistance programming; and paying more attention to risks to the sustainability of outputs and outcomes and their mitigation during project preparation and implementation.