Resumen
Decisions on transport policy measures proposed by the European Union (EU) have long-term and important impacts on economy, environment and society. Transport policy measures can lock up capital for decades and cause manifold external effects ? thus, policy measures may have a tremendous scope, especially if proposed on a European level. In order to allow European policy-makers to evaluate transport polices, a strategic assessment tool is required to compute economic, environmental and social impacts of transport policies. The paper illustrates the conceptual phase of development of the strategic high-level transport policy assessment instrument HIGH-TOOL. After careful identification of user requirements, on the basis of EU policy documents and user surveys, the conception stage of the strategic transport policy assessment tool is described in terms of tool structure, scope of output indicators, transport policies covered and other key features. Besides elaborating the structure and key features of the assessment instrument, the paper demonstrates the complexity and sensitivity associated with the conception stage of the development of a policy assessment tool. Several targets of a policy assessment tool are mutually conflicting, which results in the need to carefully counter-balance these targets, under consideration of methodological and implementation-wise aspects. The paper elaborates trade-offs between different tool objectives and derives a magical polygon of targets of an assessment instrument.