Four crews of eight, consisting of professionally skilled persons, preferably high school graduates or even undergraduates with language and computer skills, are necessary for each shield. The tunnelling machine is controlled by a pilot stationed in the cabin located in the middle of the machine, to which all data on the inputs and outputs of the machine equipment is relayed. Taking the data into consideration, the pilot chooses the optimum advance rate for the shield. All of the other members of the crews have not only their specialisations, but they have to be able to stand in for each other. In addition, a common team roughly of 12, responsible for logistics support, is available on site for both shields.