# Determining the Optimal Positions of Infill Balise Groups for ERTMS/ETCS Level 1 Applications
### Literature Review  
The research and literature covering ETCS level 1 in particular is sparse. Most papers concerning ETCS focus on level 2, which uses radio to transmit the MA and updates directly to the train. The focus to date lies on determining the capacity of ETCS level 2 compared to legacy train control systems [31] and how to increase this capacity. Papers focussing on ETCS level 1 or other, spot-transmission, balise-based train control systems are rarely published. The few instances where the capacity of ETCS level 1 was calculated and compared to other ETCS levels or legacy systems often do not disclose the exact method of where and why infill balise groups were placed. A complete algorithm for determining where to optimally place infill balise groups taking the current System Requirements Specifications (SRS) into account as well as the train characteristics is not publicly available. The engineering guidelines of infrastructure managers are generally neither available to entities outside their organization nor well documented in terms of transferability to other applications. The following literature review is therefore highly limited in the number of references, as we were not able to obtain any more sources concerning the aim of our research. [PERSON] [32] defined the \"buffer time equivalent\"--elaborating on the work of [PERSON] [33]--and used it to calculate optimal distances of infill balise groups. He derived rules of thumb for the placement, as different parameters yielded similar results and ratios between the distance to the End of Authority (EOA) and the optimal placement of infill balise groups. This method unfortunately is neither fully documented nor easily accessible to and applicable by persons responsible for planning the positions of infill balise groups. Moreover, given the place in time this study has been conducted, the redesigned and from then on harmonized braking curves introduced with version 3.0.0 of the ETCS SRS at the end of 2008 were not available then. This leads to a trainable system behavior different from the one found on most traction units today. The results, therefore, cannot be fully translated and applied anymore. A study commissioned by UIC to the Institute of Transport Science at RWTH Aachen University [34] calculated the capacity consumption of trains under the supervision of different levels of ETCS on different generic lines and led to a revision of the Union Internationale des Chemins de fer/International Union of Railways (UIC) Code 406 [35]. For the base calculations of ETCS level 1, one infill balise group was placed at the indication point of the train with the longest braking distance. In another scenario, a second infill balise group was added 400 m ahead of each main signal. Compared to level 2, the scenario of level 1 with one additional infill balise group proved to be between 3% and 12% worse in terms of capacity. The authors note that the practical benefit of level 2 might be higher with increasing variance of train characteristics and therefore braking distances. As further scenarios with varying numbers and positions of infill balise groups were not investigated, and major change requests were implemented in the ETCS specifications--especially concerning the calculation of the braking curves--additional research might be able to clear up the picture as to when each ETCS level performs better than the other. In a following study by VIA Consulting & Development GmbH from Aachen on behalf of UIC, the capacity effects of ETCS on railway nodes were investigated [36]. Once again, the maximum number of infill balise groups in level 1 was set to two. Their positions were set at the maximum Indication Point (IP) and--if two infill balise groups were assumed-- additionally at the mean IP of the trains covered. All scenarios covering level 2 implemented speed changes at the switch, whereas level 1 scenarios did not, although ETCS level 1 Full Supervision is fully capable of that.