Ballasted Railway Track–Bridge Transition Zone Monitoring Methods: Recent Developments, Challenges, and Prospects

Many researchers have studied the dynamic response of ballasted railway track–bridge transition zones (RTBTZs) using different instrumentation systems. The primary factor contributing to the frequent abnormal dynamic behavior of the RTBTZ is differential settlement between the earthworks and structures, which is the main target for RTBTZ monitoring. These settlements result in an uneven longitudinal rail profile in the foundation and embankment soils, and in the upper layers (ballast, subballast, and form layer). This paper provides a comprehensive review based on potential new technologies for railway infrastructure monitoring. Limitations of different monitoring systems such as point scale monitoring, the sensor’s long-term performance, different sensors for different output responses, and developing simplified numerical modeling based on recorded data are discussed. In addition, opportunities to conduct efficient monitoring using a new generation of sensors such as fiber optic sensors, smart self-sensing sensors, microelectromechanical system (MEMS) sensors, wireless sensing ballast particles (SmartRock), large-scale sensoring, and remote sensing techniques such as drones and light detection and ranging (LiDar) are presented.