To install the continuous welded rail (CWR) on the viaduct, it is necessary to consider the accumulated axial force owing to temperature difference and the additional force of the rail exerted by the track-bridge expansion as a result of temperature difference, the so-called track-bridge interaction. This paper used A-thermal fiber bragg grating (FBG) sensors which do not need the temperature compensation, and electronic sensors as monitoring instruments to detect performance changes in CWR axial force. These optical fiber sensors coupled with the developed track axial force calculation software and monitoring platforms calculate the axial force distribution along the track to be monitored. To better understand the influence of the change in the bridge's structure expansion and the change in concrete slab strain on track axial forces, sensors are set up at bridge expansion joints (EJs), rail ends, and concrete slab beds. Monitoring results show that optic fiber sensors provide sensitive, clear, and stable signals. They are also durable and appropriate for long-term monitoring, providing a complete track safety warning system. DOI: 10.1061/(ASCE)CF.1943-5509.0000186. (C) 2011 American Society of Civil Engineers.