Determination of Moving Chord Length for Determining the Curvature of In-Service Railway Track

The paper deals with the still unexplained issue of the choice of chord length, which will be the most benefi cial when determining the horizontal curvature of railway track with the use of the moving chord method. In the railway track – with an incorrect choice of the chord length – the horizontal track deformations and coordinate measurement error may cause irregular curvature diagrams, which will be difficult to interpret. The study analysed three test geometric layouts adapted to the speeds of 80 km/h, 120 km/h and 160 km/h (the radii of circular curves determined as a result of the curvature estimation performed were approximately 410 m, 880 m and 1480 m, respectively). The lengths of the moving chord in the range of 10÷50 m were considered. On the basis of the conducted analysis, it was unequivocally demonstrated that the chord length used to determine the curvature in the railway track should depend on the value of the radius of the circular curve. Approximate lengths lc were proposed depending on the range of the RCA radius. The adaptation of the moving chord method to the adopted measurement procedure presented in this paper and the way of using the obtained curvature diagram, provide the appropriate application basics.