New Delhi:Railways has finally selected two firms for installing the much awaited Train Collision Avoidance System (TCAS), the safety mechanism to prevent accidents, in the 200-km-long Vikarabad-Bidar section as a pilot project.Medha Servo and Kernex Microsystems were selected among six contenders, including a few multinational companies, by the Research, Designs and Standard Organisation (RDSO) of the Indian Railways on behalf of the Railway Board, a senior Railway Ministry official said.