## 4 Industry 4.0 Concept in Railway Transportation
### Resilience Improvement Measures and Inspection of Critical Infrastructure
The timetable design is obviously a trade-off between the opposing requirements of stability and feasibility, and robustness and resilience, wherein the former requirements are typically met by using deterministic traffic models, whereas the latter require a stochastic-oriented modelling approach [207]. Other methodologies that are typically used in the resilience assessment of low-level and small-scale problems may include the use of dedicated traffic simulation suites, such as the Simulation of Urban Mobility (SUMO) [208] and the hardware-in-the-loop (HIL) approach, to validate the simulation results [209]. Naturally, special attention needs to be paid to cybersecurity challenges associated with the utilisation of IoT-based technologies and the overall cyber-physical system complexity, cloud services and interconnected infrastructure, and remote access security measures to prevent or alleviate the hazard of cyber threats and to ensure the availability and continuity of railway services [210]. A possible example is radio unavailability in tunnels and logistics facilities, and the presence of local radio interference or intentional jamming that prevents wireless communication between moving or stationary traffic subjects. The latter problem may be solved by using spread-spectrum (channel hopping) communications, wherein channel selection may be based on the game theory approach [211]. These aspects may be of particular importance when high-speed railway signalling equipment is concerned [212], as well as in the case of the transport of hazardous materials, whose routing needs to be carefully planned and executed to minimise the transportation risks [213]. Another crucial aspect of railway transportation system resilience is the comprehensive inspection, surveillance, and supervision of critical railway infrastructure, such as tracks [192; 194]; overhead power supply lines [192]; power stations, communication, and signalling equipment [214]; and tunnels [179], bridges, and viaducts [215]. To that end, reference [196] illustrates how the use of numerous inexpensive narrow-band remote sensors can improve railway transportation safety in the presence of varying tractions due to the variability of atmospheric conditions (cf. also Figure 7). To automate the surveillance and inspection processes, novel image acquisition methods using LIDAR-based photogrammetry are commonly used [187; 216] along with high-definition (HD) video cameras [215] and thermal imaging using forward-looking infrared (FLIR) cameras (Figure 16a). These are increasingly being mounted on UAV-based platforms to scan the terrain, buildings, and other parts of railway infrastructure [217], as illustrated in Figure 16b. The main advantage of UAVs compared to conventional means of surveillance is that one UAV can carry high-performance sensors and cover a very geographically large area using mobile data connection for data transmission, while a conventional surveillance system requires much more expensive information, communication, and energy infrastructure, a larger number of sensors to cover the entire area that should be monitored [218] (cf. Figure 16a,b), and possible different transmission systems for high and low data rate sensors. However, when UAVs are used for surveillance, especially during long missions, there is a certain risk of collision with the surrounding terrain or other aircraft, as indicated in [219]. Reference [219] analyses different collision risk sources and possible outcomes and recommends the utilisation of an emergency parachute for a UAV in order to mitigate the risk of propulsion failure and the loss of UAV control. To extend the aerial coverage of the railway infrastructure, hybrid propulsion technologies may be considered for the surveillance UAVs, such as the internal combustion engine-generator set coupled with the auxiliary battery energy storage system.