This article discusses the consequences of splitting multidisciplinary rail infrastructure projects into multiple design and/or construction contracts. Signalling is one part of a project that is often contracted separately, as work on this aspect takes place over much of the project life-cycle and only a small number of specialized firms are able to design and build signalling systems. When a project is split up, there is the risk that the various parts will not match up as they should at the end of the project. The risks inherent to splitting off the signalling aspects of the project emanate in particular from the large number of interfaces between signalling and other areas of the same project. This article will discuss the most significant of the risks inherent to splitting up project segments – especially signalling – and how these risks can be controlled by means of interface management. We shall also examine the various roles of an interface manager. A new tool will be presented that can predict the risks involved in splitting a project, before those splits are carried out. We shall conclude with a number of real-life examples and an overview of the added value of an interface manager.