The Kokkola – Ylivieska double track project is one of the most comprehensive signalling system projects ever implemented in Finland. It covers the modernisation of the existing track and the signalling system for the newtrack being constructed next to it. The total length of the line section is approximately80 kilometres. The signalling system project will be carried outin three main phases over five years. It includes over 20 subprojects to be commissioned during a single total traffic break of less than 24 hours when the new tracks will be connected to the old ones and the new system will be commissioned as a whole. A large number of construction companies and representatives of various fields are simultaneously working at the site and partially overlapping each other. The importance of meticulous preplanning and coordination is emphasised in a project in which safety cannot be compromised and the continuously running train traffic sets the preconditions for the construction work.