Of the many requirements modern railways must meet, those of safety, speed, efficiency and cost-effectiveness are paramount. These requirements have been the driving force for railway engineers to develop new and innovative track structures. Conventional track structures consisting of a superstructure resting on a ballast bed have over time given way to ballastless track structures. These innovative structures, though often costly to construct, remain feasible due to the decreased maintenance requirements. Lower maintenance requirements lead to fewer interruptions to traffic, and considerable cost savings over the design life of the structure.