Due to the existing use and shortage of railway capacity, the reliability of tain operations is threatened. An increasing market demand requires fitting even more services in the railway system leading to upgraded scenarios.An analysis based on the Blocking Time Theory is used to asses the different alternatives addressing to the signalling system and infrastructural extensions to upgrade the capacity of double_track line between Den Haag and Rotterdam. Computations carried out using a simulation tool showed that signalling improvements appear not to give a substantial contribution to increase the capacity. On the other hand, removing the capacity bottlenecks located at stations and merging points by means of second-track extensions per line direction might achieve a significant reduction of track occupations in order to fit the timetable with additional trains, keeping or even improving the existing timetable stability.Other solutions are analysed referring to new timetable concepts based on dwell time optimization or speed homogenization due to their proved influence on the existing critical sections.