Inspecting crossing geometry

Abstract

Turnouts allow trains to change from one track to another. Therefore, they are an essential part of infrastructure to create and operate a railway network. This project focuses on the (common) crossing; the part of the turnout where the inner rails cross through one another. Because of the shape of the wheels, it is necessary to create a discontinuity in the rail at this location. As a consequence, wheels experience a disturbed support which causes wear, deformation and fatigue on the crossing. In the Netherlands, this problem has a high priority. This is because the Dutch railway network is unique in two ways; it is very dense and it has a high utilisation. Per km2 of land area, the Netherlands has the second highest amount of track length (right after Switzerland). Per km of track, the Netherlands has the second highest amount of passenger kilometres (right after Japan). The consequence is a set of 7000 that are relatively heavy loaded.
In order to extend the lifetime of these crossings, they have to be monitored and maintained. In present practise, some deformations have to be cut off and cracks have to be ground away. This ensures safe wheel passages and prevents fatigue related failures. Such practises are described well, within the current norms.
A less clear topic however, is the maintenance of geometry. Geometry is defined as the cross-sectional shape of the rail. As soon as the geometry of a crossing changes due to deformation and wear, the vehicle behaviour is influenced. Unfavourable geometry can lead to a big amplification of dynamic forces from passing wheelsets. For this reason, maintainers seek for favourable ways to assess and control the shape of worn/deformed crossings.