# Evaluating Short-Wave Effects in Railway Track Using the Rail Surface Signal
## 1 Introduction  
The track quality not only directly affects the safe operation of the train [1] but also its interaction performance with infrastructures [2]. Irregularities of the track lead to an increased force input for both the vehicle and the track itself, are in this way self-reinforcing and therefore increase without appropriate measures. On the infrastructure side, the interactions are determined by the amplitude and the wavelength of the track discontinuity [3]. Effects with short wavelengths can cause rail fractures and are therefore relevant to safety [4]; at the same time, the elimination of the effects is cost-relevant, as [PERSON] demonstrates on squats [5]. Noise problems caused by short-wave effects, as discussed by [PERSON] [6], can reduce the attractiveness of the railway system for passengers and residents. In addition, according to [PERSON], the increased force effect due to the high-frequency excitation of vehicles leads to increased deterioration processes of the entire track [7]. To make short-wave effects measurable, measurement systems with high-frequency sampling rates have to be used. Historically, measurement systems used by most infrastructure operators evaluate the infrastructure in longer wavelength ranges. The European standard EN 13848-1 covers three wavelength ranges: D1 (3-25 m), D2 (25-70 m) and D3 (70-150 m) [8]. D3 is only relevant for speeds above 250 km/h, while D1 and D2 must be used obligatorily for asset management. The annex of the standard also refers to possiblemeasurement methods for short-wave effects, primarily by means of axle box accelerations. However, this part of the standard is declared to be purely informative and is not specified as a minimum requirement. A requirement that comes with the handling of short-wave and thus punctual faults is exact positioning. Since the timely development of a quality parameter must be considered for a meaningful condition assessment, various measurement runs must be positioned to each other in sufficient quality. Historically, location deviations of measurement runs in the meter scale were justifiable, as characteristic values were calculated over a length of 100 m and more [9]. In addition, today the condition of the track geometry of open track is successfully assessed in this way. Even if the longitudinal level itself is used as a quality index [10], positioning accuracies of 25 cm are sufficient, since this parameter is usually not stored in a higher resolution anyway. To evaluate short-wave effects, we need relative positioning accuracies in the centimeter to millimeter scale. The sector's experience in describing short-wave effects with measuring data is relatively low due to these issues of missing precise position. Nevertheless, also today these effects are assessed by different methods. The most common way of evaluating short-wave effects (the term \"short-wave effect\" is defined differently in various works. For this paper, the term is used for all effects of the railway track whose characteristics have a wavelength of less than 1 m. This includes any kind of corrugations, squats, welding joints, insulated joints, switch components, rail breaks, skid marks, indentations, break-outs at the running edge and machining errors) is still visual in-track inspection. Due to the high competence of the responsible track staff, visual inspection still delivers the most reliable results. Nevertheless, significant disadvantages of visual inspection occur. Regular route inspections are carried out at walking pace and are therefore very slow, resulting in high costs on the one hand and low frequencies on the other one. As the trend moves towards less available staff, track condition assessment can no longer be carried by track inspections only in the future. In addition, as the number of trains increases, entering the danger zone must be reduced to a minimum. One very broad investigated method for the evaluation of short-wave effects are axle box accelerations.