# Influence of the Analytical Segment Length on the Tram Track Quality Assessment
## 2 Materials and Methods
### Defining the Geometry Parameters Limit Values  
The W index represents the number of exceedances of the allowed tolerances of track geometry parameters on a track segment. If available, these tolerances should be taken from the applicable regulations; otherwise, it is necessary to apply the limits defined by the European Standard EN 13848-5 [34]. As the internal regulations [23] defined only the permissible deviations of track gauge and cross-level immediately after track construction and the gauge values that define the need for track immanent reconstruction, the decision was made to consult the European Standard EN 13848-5, and Deliverable 2.4 of the Urban Rail Transport project [22]. This EU-funded research project aimed to develop, test, and validate innovative solutions for public-transport urban railway tracks such as tram and metro. The project goals also included the development of innovative and harmonized preventive and predictive track maintenance methods based on EN 13848-5. The project resulted in the draft of a standard that attempts to find typical safety limits for European urban transit networks following the development of high-speed and conventional standard-gauge railways and broad-gauge railways. EN 13848-5 defines three primary limit levels where: (1) Alert Limit (AL) refers to the values which, if exceeded, require that the track geometry condition is analyzed and considered in the regularly planned maintenance operations; (2) Intervention Limit (IL) denotes the value whose exceedance calls for the corrective maintenance so that the immediate action limit shall not be reached before the next inspection; and (3) Immediate Action Limit (IAL) denotes the value whose exceedance calls for action to reduce the risk of derailment to some acceptable level. Limits are prescribed as a speed function for the nominal track gauges 1435 mm, 1524 mm, and 1668 mm [34]. Furthermore, the limit values are given for a loaded track as defined in EN 13848-1 [33]. Table 2 presents the prescribed AL, IL, and IAL for line speeds up to 80 kph. Limit values for geometry parameters measured in loaded track conditions given in Deliverable 2.4 of the Urban Rail Transport project [22] are presented in Table 3. They are defined for three primary limit levels where AL refers to ride-comfort issues, IL refers to maintenance cost-effectiveness issues, and IAL refers to safety issues. As measurements of the track geometry parameters in the City of Osijek were performed in unloaded track conditions, it was impossible to determine the synthesized W by directly applying the limits prescribed by the European Standard or Urban Track project. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter/Defectiveness** & **AL** & **IL** & **IAL** \\ \hline Gauge (mm) & \(-7.0\)/ \(+25.0\) & \(-9.0\)/ \(+30.0\) & \(-11.0\)/ \(+35.0\) \\ Cross level (mm) & \(-20.0\)/ \(+20.0\) & \(-20.0\)/ \(+20.0\) & \(-20.0\)/ \(+20.0\) \\ Twist (mm/m) & \(-4.0\)/ \(+4.0\) & \(-5.0\)/ \(+5.0\) & \(-7.0\)/ \(+7.0\) \\ Horizontal alignment (mm) & \(-12.0\)/ \(+12.0\) & \(-15.0\)/ \(+15.0\) & \(-22.0\)/ \(+22.0\) \\ Longitudinal level (mm) & \(-12.0\)/ \(+12.0\) & \(-17.0\)/ \(+17.0\) & \(-28.0\)/ \(+28.0\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Alert Limits (AL), Intervention Limits (IL), and Immediate Action Limits (IAL) for line speeds of up to 80 kph according to EN 13848-5 [34]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter/Defectiveness** & **AL** & **IL** & **IAL** \\ \hline Gauge (mm) & \(-3.0\)/ \(+22.0\) & \(-5.0\)/ \(+30.0\) & \(-5.0\)/ \(+30.0\) \\ Cross level (mm) & \(-13.0\)/ \(+13.0\) & \(-14.0\)/ \(+14.0\) & \(-16.0\)/ \(+16.0\) \\ Twist (mm/m) & to be defined following stiffness and constructional characteristics of the running gear & & \\ Horizontal alignment (mm) & \(-14.0\)/ \(+14.0\) & \(-16.0\)/ \(+16.0\) & \(-22.0\)/ \(+22.0\) \\ Longitudinal level (mm) & \(-18.0\)/ \(+18.0\) & \(-20.0\)/ \(+20.0\) & \(-29.0\)/ \(+29.0\) \\ \hline \hline \end{tabular}
\end{table}