## 5 Conclusions and Future Work  
In this paper, on the basis of the field test in which the dynamic performances of the low-floor train passing the no. 6 switch in the rail transit depot, the track alignment, wheel treads and rail profiles were measured, and a corresponding low-floor train-turnout switch coupling dynamic model considering the alignment irregularity ahead of the switch was established. The model takes the coupling effect of the train and turnout into full consideration, and the simulated results were validated with measured results. On this basis, the influences of the train speed, wheel-rail friction coefficient and alignment optimization on the dynamic performance of low-floor trains passing the turnout switch were investigated. The results show that:  
1. When there is bad alignment irregularity in the tangent before the turnout, the wheel-rail dynamic performance in the tangent is worse than that in the switch; the dynamic indexes of the integrated wheelset and the independently rotating wheelset increase with the train speed increasing, but at different increase rates. In the switch, the dynamic indexes of the integrated wheelset decrease first and then increase with the increase in speed, while those of independently rotating wheelset first decrease, then increase and eventually decrease.
2. The dynamic indexes of the integrated wheelset in the tangent with alignment irregularity increase with the increase in the friction coefficient, while the dynamic indexes of the independently rotating wheelset will increase both under the condition of smaller and larger friction coefficients, but tend to decrease under an intermediate friction coefficient. The vertical force of the motor wheel in the switch zone exceeds that in the tangent as the friction coefficient increases. The variation trends of the derailment coefficient and wheel load reduction are inconsistent with the trends of the lateral force and vertical force, respectively. In the switch, the dynamic indexes of both wheelsets increase as the friction coefficient increases, and the lateral force and derailment coefficient of the independently rotating wheelset increase remarkably.
3. Eliminating alignment irregularities before the switch can effectively improve the dynamic performance of the integrated wheelset in the switch, and the lateral forces of the outer wheels of these two vehicles are reduced by about 80%, the derailment coefficients are reduced by about 70%, the vertical force reduced by about 10-20% and the wheel load is reduced by approximately 30%. Due to keeping in flange contact with the outer rail entering the switch, the independent wheelset has a rather limited promotion in dynamic performance when passing the switch.  
**Author Contributions:** Conceptualization, X.J. and X.Y.; methodology, X.J.; software, X.J.; validation, X.J., X.Y. and G.S.; formal analysis, X.J. and X.Y.; investigation, X.J.; resources, X.Y.; data curation, X.J. and X.Y.; writing--original draft preparation, X.J., X.Y. and G.S.; writing--review and editing, X.J., X.Y. and G.S.; visualization, X.J.; supervision, X.J.; project administration, X.Y. and G.S.; funding acquisition, X.J., X.Y. and G.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 51778484.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article.  
**Conflicts of Interest:** The authors declare no conflict of interest.