This article presents the intermediate design phase for the development of Gautrain railway project in South Africa. This phase is specific to concession and develops the project between the Letter of Intent and Financial Close. It is described in terms of objectives, organisation, technical aspects, and more important interface and integration. Gautrain Rail project consists of developing, designing, constructing, operating and maintaining a 77km long railway line to provide domestic and airport train services, together with a dedicated bus network servicing a radius of 10km around each of the 10 stations, and 9,000 specific parking spaces within the station precincts. In this comprehensive and complex project, Bouygues TP is ensuring the technical leadership.