# Full-Scale Experimental Investigation of the Interaction between Trains and Tunnels
## 4 Conclusions  
This works represents a contribution to the analysis of overpressures arising when a train crosses a tunnel. The phenomenon is one of the most challenging aspects, if an increase both in the operating speed and in the capacity of a HS line are considered. Furthermore, it is lacking in deep validation, even if it is codified within standards and it can be studied by means of specific tools. The possibility to perform wide experimental campaigns on different sections of the Italian HS line by measuring on board and at trackside and by recording data for both testing and commercial trains allowed to better investigate the issue of tunnel overpressures and to present new applications, such as the mixed traffic operation.  
Full-scale experimental activity within the railway system is a very demanding and challenging task since many actors are involved (infrastructure managers, trains operators, trains manufacturers) and, as a consequence, few data are available in the literature. Moreover, few areas are usually left to research since most of the experimental work is based on the application of standard procedures to well confined topics. Therefore, the research field is usually limited to model scale reproductions in laboratory test rigs. Nevertheless, this work takes advantage from the purpose to increase the Italian HS line performance (both speed and capacity) by involving universities not only in the preliminary feasibility study but also in the experimental validation of the project.  
Thanks to the wide availability of experimental data, it is possible to highlight some criticalities that can be summarized in two main points:  
Figure 17: Example of the behavior of the HVAC shutters of the sealed train and corresponding pressure evolution.  
* The initial conditions within the tunnel highly modifies the pressure signature;
* The position of the sensors is fundamental to properly estimate the pressure loads.  
According to the proposed work and as future developments, existing standards should be revised by accordingly implementing at least these aspects:  
* A limit value on the flow speed or a corrective formula that also takes into account environmental data, e.g., pressure, temperature, and density, should be defined;
* Since the 10 kPa health criterion could be exceeded for a few tenths of seconds due to fluctuations in the wake region, deeper specifications on this topic are needed;
* To properly estimate the aerodynamic loads, the measurement of the external pressure on both sides and the internal pressure in at least one point per car should be specified.  
Based on the presented results, a new measurement campaign has been planned with the intention of measuring the environmental parameters also in the tunnel and of finding a corrective formula for the pressure signature. On the other hand, a new 1-D code is being developed and it will consider the characteristics of different types of trains and the specific effects of the TNS in case of crossing.  
Conceptualization, C.S., T.A., D.R. and P.S.; Data curation, C.S., T.A., E.B. and P.S.; Formal analysis, T.A. and E.B.; Funding acquisition, D.R.; Investigation, C.S.; Project administration, D.R.; Resources, G.T.; Supervision, D.R. and G.T.; Writing--original draft, C.S.; Writing--review & editing, E.B., D.R. and G.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.