# Long Term Effects of Reduced Track Tamping Works
## 1 Introduction  
Tamping is the most important and most costly maintenance action in ballasted railway track. Since maintenance budgets are seldomly sufficient, tamping, despite its dominating share, has to be minimized. This often starts with reduced tamping length, accompanied by shorter track closures, an effect that is also welcomed by the operation departments in order to keep availability of track high and thus supporting the punctuality goals of the infrastructure managers. At its highest degree, the reduction of tamping leads to an almost total abandoning of line-tamping by establishing a spot taming only regime. Single failures in track geometry are safety relevant, thus subject to normative limit values (see EN13848-3) and consequently need to be tamped in any case. This strategy change leads to relevant short term savings in the maintenance budgets but also to a reduction of through-going track quality. This induces a loss in service life in the long term, a fact to be shown in this paper based on measuring data. As service life triggers renewal, the budgets for necessary reinvestment increase in the long term perspective. Depreciation is the dominating cost position in the life cycle cost of track. It turns out that the short term savings are by far lower than the long term costs. This is common knowledge but as there is no data-based evidence, strategies frequently change between a short-term savings goal and a sustainability focused one. This paper provides a data-based model depictingthe effects of different damping regimes and their cost effects in order to identify the best strategy to be followed. Spot damping in the evaluation which follows means correction in single failures of track geometry, more precisely in longitudinal level (LL). This reactive maintenance is driven by (immediate) action limits. The European Standard EN13848-3 provides three different, speed dependent limit values: the alert limit (AL), the intervention limit (IL), and the immediate intervention limit (IAL). Reaching the IAL necessitates an immediate measure ensuring safe train operation. As maintenance cannot be executed immediately after measuring the car run, infrastructure managers have only one option: setting a speed restriction (lower speed comes with a lower IAL) until the point in time of maintenance action. Reactive maintenance can be subject to a certain optimization in focusing on the AL and IL, though increasing maintenance demand. Another possibility is to predict the time-to-IAL. This needs a precisely positioned longitudinal level as the confidence interval of prediction again triggers the maintenance amount. Line-tamping ensures through-going quality assessed by (mainly) standard deviation (SD) of LL [1; 2]. As investigations show [3], this parameter is very well suited to fulfil this task. EN13848-3 defines an IAL only at a very high level of 5 mm, where AL and IL do not exist. Line tamping needs to ensure both low dynamic forces applied to track and a certain riding comfort for passenger trains. Intervention levels are thus defined by infrastructure managers according to their boundary conditions, if they are defined at all. Assessing both single failures and through-going track quality is unfortunately not possible in using more holistic indices describing track quality [4; 5; 6], so these assessment needs to be separated. Assessing track geometry, its behavior over time and the recovery of track quality after track tamping requires intensive data analysis. Firstly, especially when looking at the raw signal \"longitudinal level\", measuring signals of different car runs need to be precisely positioned. A precise and efficient approach is one subject to the CoMPAcT-algorithm developed by [PERSON] [7]. The deterioration of geometrical quality over time was analyzed by several authors and many different models have been published over the years [8; 9].