In recent years there has been an increasing concern with the performance of public sector institutions. Such concern is reflected, for example, in the work of the Audit Commission and National Audit Office which is directed at improving the effectiveness and efficiency of local and national government institutions in the context of a broader programme to reduce the scale of resources to be allocatedthrough public sector decision making. This concern with effective decision making has intensified debate about the potential role of the application of science in improved decision-aiding techniques. This debate has a long history, but has gained a renewed currency with the development and refinement ofthe power of information technology (IT) with its enhanced capacity to permit the application of analysis in support of decision making. \ud \ud However, there exists a considerable degree of controversy about the role of scientific knowledge, analytical techniques and IT methods, and of the experts who apply them, in 'improving' decision making. The 'rationalist' extreme was perhaps epitomised by Yehezkel Drorls advocacy of 'policy sciences' in his concern with "...the contribution of systematic knowledge, structured rationality and organized creativity to better policy making ..." in which "...policy sciences is essential for improvement of the human condition.. ."1. Opponents of this view emphasise the role of value-conditioned judgement and of political processes in particular social and institutional contexts; we can recall Sir Geoffrey Vickers' insight to the effect that ". . .even the simplest of the policy maker's problems is not to be resolved by even the most complicated of his calculations. . . "2 \ud \ud Our research is located in this controversial area and is concerned with the scope for 'improving1 decision making about major roads investment projects through the use of computerised decision support systems (DSS) based upon the framework approach to scheme appraisal. Following the work of the Leitch Committee and SACTRAthe framework approach is now well-established as the means for the applicatipn of the cost-benefit form of evaluation to major road schemes. However, in combining and comparing a wide range of impacts, only some of which are readily quantifiable, the framework requires judgement to be exercised in determining relative weights and trade-offs between impacts and affected groups. Our research aims to examine the potential role of a decision support system in helping to clarify the basis upon which such judgement is exercised. \ud \ud (Continues..