In advanced rail traffic operations with train speeds of over 160km/h, uninterrupted train control and protection functions are critically necessary. In addition to visual signalling techniques, the train driver must on his display see trustworthy information on the occupation status of the track section ahead, as well as on the next signal.

Owing to non-uniform developments in the various national railway systems, different systems with impact on the conduct of train traffic have developed in the respective countries. So-called track-status report systems are installed to determine and report on whether or not rolling stock is occupying defined track sections ahead of a train. These systems work on the basis of DC circuits or axle counters, depending on requirements. The UM71 DC circuit system feeds an audio-frequency signal into both rails.

A certain, specified minimum sound-signal level is required to assure correct reporting of the occupation status of a track section. The impedance in the rails and the track connections attenuate these signals, in accordance with the distance between transmitters and receivers. In addition, the frequencies used in the system produce characteristic inductive voltage losses. These phenomena make it necessary to install specified transverse capacitance between the two rails, at regular intervals.

In ballastless track systems with steel reinforcement in the concrete, the magnetic fields of the audio-frequency rail currents induce a voltage in the reinforcement rods running parallel to the track axis. Closed short-circuit current paths can develop via the transverse reinforcement rods, and can lead to additional signal attenuation.

Pfleiderer track systems has developed the following solution for Asian application of the RHEDA 2000® ballastless track system. The bottom chord and the lower part of the diagonal struts of the lattice girder are covered by a long-life coating that provides effective electrical insulation. This layer prevents direct steel-to-steel contact. Prefabricated plastic clips insulate and provide secure fastening at the transitions of longitudinal and transverse reinforcing bars.

The manufacturer of the UM71 DC circuit has very recently tested this solution on a test track built for this purpose, and has verified its effectiveness. The negative effects of the track reinforcement are almost completely eliminated, and the effective range of train-detection signalling reports is very nearly the same as for ballasted track.

The RHEDA 2000® Ballastless Track System

The RHEDA 2000® ballastless track system is currently the most advanced development in the RHEDA family. The two most essential modifications over the previous models consist of the following: application of an especially matched bi-block lattice-truss sleeper, as well as integration of infill concrete and the reinforced trough slab into a unified, monolithic track-support layer. The sleeper with non-prestressed-reinforcement – together with the concrete bed that encloses it – forms an extensively monolithic structure that can be designed with minimally low construction heights for installation on all track substructures suitable for ballastless systems.

Owing to its end-to-end systems engineering, RHEDA 2000® is highly effectively suited for implementation on earth sub-base, over bridges, in tunnels, as well as for turnouts. In areas sensitive to vibration, RHEDA 2000® can also be implemented in conjunction with a spring-mass system. The mass of the concrete track system, supported on elastic damping elements, effectively reduces or eliminates the effects of vibrations on the track surroundings.