Railways are a mass transportation system with high safety and punctuality. These strengths have been well proved by tests and evaluations. Railways are an integrated system with cars, power, signal, communication, line structures and operation. Among many safety standards of these systems, contact force between wheels and lines can be chosen since a derailment coefficient evaluated by contract force is the most important fact that decides the safety of railways. Especially regarding express trains, since they run twice faster than conventional ones, the evaluation of a derailment coefficient is more important than any other criteria. Currently, Korean express trains between Seoul and Pusan use the same stations as conventional trains in Daejeon and Dong-Daegu; therefore, express trains run on conventional lines from express lines. This paper describes test results acquired by increasing the train speed where express lines and conventional lines are connected. Test results tell that it is safe with under 0.8 derailment coefficient and running time is reduced by 10~30 seconds in each section.