Ballastless track

A ballastless track or slab track is a type of railway track infrastructure in which the traditional elastic combination of ties/sleepers and ballast is replaced by a rigid construction of concrete or asphalt. In ballastless tracks, the rails are rigidly fastened to special types of concrete ties/sleepers that are themselves set in concrete. Ballastless tracks therefore offer a high consistency in track geometry, the adjusting of which is not possible after the concreting of the superstructure. Therefore, ballastless tracks must be concreted within a tolerance of . The elasticity of the ballast in the traditional railway superstructure is replaced by flexibility between either the rails and the concrete ties/sleepers or the ties/sleepers and the concrete or asphalt slab as well inherent elasticity within the conglomerate of the tie/sleeper, whereas the concrete or asphalt slab is usually inelastic. The advantages of a ballastless track over a traditional superstructure are its highly consistent track geometry, its longer life span, and the reduced need for maintenance. A ballastless track’s track geometry is achieved mainly due to its relative inelasticity in comparison to a traditional superstructure that results in far fewer deformations and generally smoother running; train drivers (engineers) of the London Overground's East London Line have informally declared the Low Vibration Track system as the smoothest superstructure they have experienced. Measurements conducted in Switzerland in 2003 and 2004 showed a standard deviation of the gauge of less than . This in turn increases the track’s life span and reduces the need for maintenance. The usual preventive maintenance is limited to rail grinding, since tamping is not necessary due to the absence of ballast. Curative maintenance beyond rail replacement is required only after several decades. The Swiss Federal Railways replaced the ties/sleepers and rubber shoes of the ballastless track in the -long Heitersberg Tunnel between 2014 and 2016, whereas no maintenance of the concrete slab was necessary 39 years after the tunnel’s opening.