The ERTMS migration strategy for a railway network is often restrained by important factors such as equipping an entire train fleet, training personnel, accepting signalling asset devaluation, long out-of-service periods, capacity issues and much money. Due to organizational and technical struggles, the practical implementation planning often ends at level 2. Surprisingly, most national ERTMS implementation plans describe level 3 as the ideal and final goal, but lack a clear description on how to get there. This article clarifies the current possibilities and limitations of ERTMS level 3 and outlines a basic solution to roll out ERTMS level 3 systems quickly and gracefully on a busy existing railway network.