Estimating the Accuracy of Track-Surveying Trolley Measurements for Railway Maintenance Planning

Maintenance of the rail track plays an important role in the policies that promote railway transport in the European Union. Each member state has its own railway infrastructure manager that is regulated by the standards set by the European Committee for Standardization (CEN). The standards define three levels for the track geometric quality: the alert limit (AL), the intervention limit (IL), and the immediate action limit (IAL). In the United States, the Federal Railroad Administration (FRA) manages the railroad safety and national rail transportation policy. They classify nine classes of tracks depending on the maximum allowable speed for freight and passenger trains; each classification has its own track geometric limits from nominal values. Usually, track-survey cars are used to measure the parameters of the geometric quality of the tracks in long sectors, whereas traditional surveying methods (TSMs) or an automated measuring system based on a track-surveying trolley assisted by a robotic total station is chosen for short sectors. In this paper, the authors analyze the precision and performance obtained with the TSM and with an automatic measuring system in its different working modes (stop and go and kinematic), comparing the measured geometric values with the nominal values for a section of a track. The results indicate that TSM and stop-and-go modes yield similar precisions, so both methods can be used to detect the geometric quality levels defined in the CEN and FRA standards. In contrast, kinematic is less accurate, so there are situations where it cannot be used to determine the geometric quality levels. Finally, the authors discuss some recommendations to improve the performance and working methods with the track-surveying trolley.