in enhanced safety: Increases the resistance of the track to lateral movement Creates a homogenous bed of ballast Permits earlier relaxation of speed restrictions Eliminates non-uniform initial differential settlements caused by rail traffic Retains correct track geometry for a longer period than was achievable using tamping machines alone Vibration frequency: 30–35 Hz Working speed: 1–2 km/h Vertical pressure applied: The stabilisation achieved by one pass of a DGS is equal to that achieved by 100,000 tonnes of traffic, and allows a speed restriction of 20 km/h to be relaxed to 40 km/h Dynamic stabilisation is usually avoided on bridges or around overhead structures since there is a risk of damage to foundations. Tamping and track layouts The appropriate tamping procedures and tamping machine depends in part on the track layout. On plain track everything is fairly straight forward and any brand and model of machine can be used. But through tunnels and bridges with no ballast to tamp, special measures are needed to transition from the ballasted track to the unballasted track. An example would be the Glenbrook Tunnel Turnouts require a more complicated tamping machine with extra and adjustable tongs to cater for the extra rails and variable spacing of the sleepers. Similarly for dual gauge such as between Perth and Northam. Ideally turnouts and diamond crossings should be some distance apart so the each component can be tamped without having to immediately tamp the other components. However a majority of track components are right next to each other so that these components need to be tamped as a group in multiple small stages. Track centres determine whether one end of a crossover, consisting of two turnouts, can be tamped one at a time, with train traffic still running on the other track. Manufacturers of tamping machines Matisa Plasser & Theurer / Plasser American Banbury Amey Balfour Beatty CHZ podbijecka Harsco Tamper (company) - acquired by Harsco in 1992 Image gallery See also Ballast regulator Gandy dancer Stoneblower Track maintenance Track renewal train References Further reading Plasser and Theurer Track Geometry Maintenance Durability Seminar, Athens, 11 October 2011, Ing. Rudolf Becker "Track Compendium" DW Media group GmbH I Eurailpress External links Audio recording of tamping machine Photos of dynamic track stabilisers in the UK Photos of tampers in the UK http://s7australia.com/system7-products/rail-tamping/ Maintenance of way equipment Articles containing video clips