Specifications for bituminous materials in highway construction are continuously evolving. At an early stage, they were more intuitive and based on engineering judgement. They were called method or recipe specifications in which the client specified the materials and procedures that the contractor had to use.

In the 70s, they evolved to end-result specifications in which the contractor started to assume responsibilities for quality controls and construction methods. The clients then concentrated their activities on designing and judging the acceptance of end-results specifications on a statistical basis. This change led to the implementation of quality assurance systems.

Method specifications and end-result specifications do not guarantee performance. Therefore, there has been growing interest in developing performance specifications based on attributes affecting performance. Although this type of specification is the next logical step, other types of specifications will still be used depending on the project, because they meet the needs of industry and of clients.

This report describes, in generic terms, the evolution of client's requirements in order to achieve satisfactory performance, which include tolerances and specifications and also quality systems.

The first part of the report deals with the current ways of evaluating variability and establishing tolerances. The next chapters describe the evolution of specifications and quality systems. A series of five papers by invited experts are included to illustrate the situation in different countries. The last chapter focuses on the trend towards performance specifications and the substantial benefits that are foreseen for clients and contractors. This chapter also deals with issues that need to be addressed in implementing them.

Finally, the report contains conclusions and recommendations in favour of encouraging research and supporting programmes of full-scale trials on performance specifications.