# Quality Behaviour of Turnouts: Comparison, Problem Specification and Recommendation of Measures
## 2 Methodology
### Quality Comparison of the Analysed Turnouts  
In this part of the work, the tools described above are used for quality comparison between the five turnouts analysed. The comparison starts with vertical track geometry (cTGI, utilisation rates and twist), as these parameters are the most important indicators for maintenance planning and at the same time an indication of poor system behaviour. The temporal development of the cumulative track geometry index in vertical direction for each turnout is shown in Figure 5.  
The horizontal dashed lines represent the same quality levels as introduced in Figure 2b. Maintenance actions affecting the track geometry are represented by vertical lines, with black lines representing the tamping of each turnout, coloured solid lines representing the tamping of the respective turnout and coloured dotted lines representing local actions at critical spots. It can be seen that the average vertical track geometry of the turnouts behaves similar from 2012 to 2018.75. In the first years, track geometry deteriorates relatively quickly, but after tamping in 2014 quality of each turnout is good, and deterioration is also not excessive. A closer look at the period between 2014.5 and 2018.75 shows that two turnouts behave slightly worse than the others, namely T_R4F_21 and T_R4F_23. Their average track geometry is at a slightly higher level, and their deterioration rates are also slightly higher. Considering the daily load shown in Figure 1, this is not surprising as it is higher for these turnouts than for T_R4F_22 and T_R4F_25. However, it is surprising that T_R4F_24, which has a similar daily load to T_R4F_21/23, behaves better than T_R4F_22/25. When looking at the evolution of T_R4F_24, improvements can be seen in 2015.5 and 2017.5. Using interactive raw data visualisation confirms the assumption that there must have been additional tamping actions for this turnout. These actions cannot be explained with the available tools but do explain the quality behaviour of T_R4F_24. Due to tamping work at the end of 2018, track geometry of all turnouts besides T_R4F_21, but especially that of T_R4F_23, could be brought back to a good quality. Since then, T_R4F_21 has behaved significantly worse than the other turnouts. Even an additional tamping task in 2020 could not solve the problem. Only after a tamping task in 2022.0 could track geometry of T_R4F_21 be slightly improved. Nevertheless, the average quality of T_R4F_21 is still worse than the quality of the other turnouts. Looking at utilisation rates and twist values improves the understanding of the described development. Figure 6 shows maximum twist values over time for the turnouts examined. Figure 5: Development of the cumulative track geometry index—comparison of analysed turnouts. By including twist failures, it becomes clear why the average track geometry of turnout T_R4F_21 and turnout T_R4F_23 behaved similarly before 2018 and differently after tamping in 2018. For T_R4F_23, twist was the main problem until 2018; the alert limit was reached here. By eliminating the twist error in 2018, the main cause of poor track geometry was removed, and therefore average track geometry has improved significantly and sustainably. T_R4F_21, on the other hand, was not a problem for track workers in 2018, and no limits were reached. This is also confirmed by the utilisation rates, which are summarised in Table 1.  
The first column of the table summarises utilisation rates for the entire observation period, showing that T_R4F_21 is on average closest to the intervention limit. In addition, utilisation rates are summarised for the period between 2016 and 2018.75, the period immediately before tamping. During this period, T_R4F_23 was the most critical turnout, with utilisation rates up to 80%. T_R4F_21 is inconspicuous here. This further emphasises that T_R4F_21 appeared to be in a stable condition in 2018 with the tools available to track workers (raw signals of the longitudinal level and twist). However, this changed after 2018.