Large infrastructure systems with a life time of more than 30 years, such as telecommunication or power transmission systems, are difficult to maintain since they suffer from the end-of-life plague of software, hardware and knowledge. Large companies have traditionally tackled this problem successfully, but maybe not with complete efficiency in all cases. We find system evolution to be an increasingly interesting problem as infrastructure becomes more complicated. Our increasingly complex and advanced society demands more of the infrastructure making system evolution an interesting alternative to system replacement. From the point of view of the ISO/IEC 15288 development process we have identified life cycle issues connected to long life time scenarios and the different life cycle stages. In this paper we contribute with a modification of the utilisation and support stage in ISO/IEC 15288 into an evolution stage where a system is not only retired and replaced but rather evolved into the next generation. Using this approach changes the view of system development for this specific type of systems towards a way of incremental development, where new functions can be added at the same time as old legacy parts are replaced with functionally equivalent modules based on new hardware. We have based our solution on the experience from investigations of life cycle issues for two large infrastructure systems.