Causal Effects of Railway Track Maintenance—An Experimental Case Study of Tamping

This paper illustrates a generalisable experimental approach to assess the causal effects of track maintenance actions. In our case, we assess the causal effects of tamping on railway track geometry. The tamping was conducted during the regular autumn tamping campaign in 2022 on track section 118 of the Swedish Iron ore line “Malmbanan”. The experimental setup provided frequent measurements of track geometry closely before and after the tamping action to estimate the potential causal effects of tamping on track geometry. Damill AB provided the track geometry data through an onboard measurement system mounted on a passenger train wagon travelling the track section frequently. The system provides position, speed, and track geometry variables, such as longitudinal level and lateral alignment, through GPS, accelerometers, and gyros. We based the analysis on hypothesis testing (Welch’s two-sample t-test) to test the statistical significance of tamping effects on track geometry variables. The analysis included a segmentation of the tamped track section to form experimental units allowing the application of hypothesis testing. The frequent measurements also allow for assessing how effects change over time. The analysis established a statistically significant reduction in the standard deviation of the longitudinal level and the standard deviation of the lateral alignment of the track after tamping. The experimental approach is generalizable for assessing the causal effects of other railway track maintenance actions.