# Evaluation of Measurement Strategy for Track Side Monitoring of Railway Wheels
## 5 Conclusions  
Rail wheels are crucial components in the railway infrastructure that need to be periodically monitored to ensure safe and reliable operation. The goal of this study was to investigate the representability of a one-slice measurement strategy for railway wheel profiles with respect to wheel profile parameters. Four wheel parameters were estimated on the basis of the measurements recorded: flange height (Sh), flange width (Sd), flange slope (qR), and tread hollow (Th). There were variations in all the estimated parameters for different positions measured within the same wheel, indicating the spread of wheel profile parameters along the circumference of the wheel. In order to exclude the dependency of the measurement operator, the results of the two operators were compared and the difference between the operator dependency was low compared to the studied effect of the position along the circumference. As an initial validation of the results, measurements from a wayside monitoring system were investigated in order to see if a similar spread was visible for multiple measurements.  
On comparing the calculated range of standard deviation of the parameters estimated from measurements using handheld equipment to the same parameters measured by wayside measurement equipment, it can be concluded that the wayside measurements show a larger spread along the circumference of the wheel. A similar spread from both the  
Figure 9: Histogram of tread hollow (Th) for eight different wheels measured by the wayside wheel profile measurement system. \(X\)-axis represents the tread hollow in mm, and \(Y\)-axis represents the number of measurements recorded. The mean, standard deviation, and range of the measurements for each wheel are described below the plot.  
measurements was observed only for the hollow-wear parameter. Based on the wheels analysed in this study, the one-slice measurement strategy of a wayside wheel profile measurement system may not be adequate to estimate the wheel profile parameters for condition monitoring purposes. Multiple measurements are required to represent the parameters along the circumference of the wheel for reliable condition monitoring of the wheels. Future studies will investigate the one-slice measurement strategy from the wayside measurement system to estimate high-level parameters such as the equivalent conicity of the wheel. This study was carried out only on wheels of a particular wagon type (iron ore wagon); future studies will focus also on wheels of other wagon types including high-speed and passenger trains. In addition, the future studies will examine the evolution of the spread in wheel profile parameters with respect to wheel age.  
Conceptualization, M.R., P.C., F.T. and J.O.; methodology, M.R., P.C., F.T., U.K. and J.O.; software, M.R., P.C., F.T., C.G. and M.A.; validation, M.R., P.C., F.T. and J.O.; formal analysis, M.R., P.C., F.T. and J.O.; investigation, M.R., P.C., M.A., P.C. and F.T.; resources, M.R., M.A., U.K. and J.O.; data curation, M.R., P.C., F.T., C.G. and M.A.; writing--original draft preparation, P.C., M.R. and F.T.; writing--review and editing, M.R., P.C., F.T. and J.O.; visualization, M.R., P.C. and F.T.; supervision, M.R., U.K. and J.O. All authors have read and agreed to the published version of the manuscript.  
This study was supported and funded by the Lulea Railway Research Centre (JVTC) and Traifikverket (Swedish Transport Administration). The study has been carried out within the strategic innovation program InfraSweden2030, supported by Vinnova, Formas, and Energimyndigheten, and the Shift2 Rail project IN2 SMART.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.