The continuous increasing demand of public transportation capacity requires the railway network operating in tight schedule. The high transporting volumes not only aggravate the degradation of railway infrastructure but also shorten the time for maintenance. Well-arranged infrastructure maintenance contributes to the budget reduction and reliability improvement. With the purpose of key parameters investigation in the turnout crossing degradation process, a series of subsequent measurements using instrumented crossing system (ESAH-M) on a 1:15 railway turnout at various stages were performed. The results indicate that wheel/rail impact area narrowed with deepened rail wear. This narrowing is a signal of rail damage. Frequency band pass filtered results describe the condition development of different structures in the turnout crossing section in the test period. Series of more systematic crossing measurements are in progress in a test section in the Netherlands. The ultimate purpose of this study is to form the crossing degradation function to be implemented in the structural health monitoring system (SHMS) for railway turnouts developed at the TU Delft.