Impact-based planning evaluation: Advancing normative criteria for policy analysis

Planning decisions have considerable impacts on both natural and built environments. The impacts of these decisions may remain for many decades and many are irreversible. In order to gain a better understanding of these long-standing impacts, planners require a systematic approach to evaluate the planning policy instruments utilised. The literature on planning evaluation shows that most studies have taken a conformance-based evaluation approach, where the success of a planning policy instrument is based on the degree of conformity between the policy outcomes and its intended objectives. While evaluating such criteria is necessary, it is hardly ever sufficient largely because of unintended effects. This paper proposes an impact-based approach to planning evaluation that incorporates all the impacts, intended and otherwise, that a planning policy instrument may bring about, irrespective of the initial objectives of the policy. Using a number of economic and planning theories, this paper argues that, in addition to conformance and performance, other normative evaluation criteria, such as, efficiency, equity, social and political acceptability, and institutional arrangements, should be included to emphasise the importance of planning decisions and their substantial impacts on quality of life, social justice, and sustainability.