The Berlin S-Bahn Train Control System - (ZBS) - is a train protection system based on Eurobalises that is designed for the specific requirements of the S-Bahn Berlin rapid transit rail network. It is able to gradually replace the old system based on train stops with overlap safety. The conversion will be finished on the subnetwork Stadtbahn until the end of 2020, on the subnetwork Nord-Süd until the end of 2023 and on the subnetwork Ring until the end of 2025. History The Berlin S-Bahn commuter rail system has its own tracks that is completely separate from the national rail network although most lines run in parallel with the normal railways. Although a heavy rail system the vehicle fleet is specialized for the Berlin rail network with its closest cousins in the S-Bahn Hamburg (which switched to 1200 Volt however instead of 750 Volt third rail in Berlin). Berlin was among the first to introduce an automated train protection system based on metal bar at the height of the first bogie where the trip cock is placed. The metal bar (also named "Streckenanschlag" / track stop collar) folds away to allow passing. If the metal bar is up it will also catch the train by sliding along the outer frame. The train stops are installed at some distance before the actual critical point (junction, station) so that with an assumed maximum speed the train can be halted. The old system had worked for almost a century although there were a number of exceptions - notably the train speed is not controlled at all and the train stops have no function for a train passing at higher speed. To improve safety the S-Bahn Berlin GmbH (train operator), DB Netz AG (rail track operator) and Siemens Transportation System (train system manufacturer) started research on a system based on ETCS Level 1. The development was done in parallel with the evolution of ETCS since the mid-1990s and the results were first shown on the InnoTrans 2002 fair. In August 2007 a contract with Siemens was closed on the delivery of cab signaling for 600 trains and the 332 km wayside signaling at a cost of 130 million Euro. The installation were to be performed in 20 stages over a period starting in 2010 until 2015. The first activation in daily routine had been scheduled for 11 October 2011 on the S1 line -