# Interdisciplinary Urban Tunnel Control within Smart Cities
## 2 Systemic Approach to Urban Road Tunnel  
### Tunnel and Its Neighborhood  
In the literature, a tunnel is often described as a complex system. Even the World Road Association (PIARC) in its PIARC Road Tunnels Manual [2] from 2019 dedicated an entire chapter to the topics of complexity. It is called \"TUNNEL: A COMPLEX SYSTEM\". The authors claim that \"_A tunnel constitutes a complex system which is the result of the interaction of very many parameters. These parameters can be gathered by subsets._\" This is certainly correct. A tunnel consists of many different subsystems and components that interact with each other. Can we, however, claim that it truly is a complex system? Let us look at classification based on complexity theory. [PERSON] and [PERSON] [3] provide seven criteria a system shall fulfil in order to be considered a complex system. In the following paragraphs, we will provide these criteria together with a discussion addressing the road tunnels in particular:  
1. Connectivity--A complex system consists of a large number of diverse components, known as Agents, which are richly interconnected. Tunnels consist of different components and subsystems. We can perceive all of the different sensors and actuators as agents. It cannot be, however, claimed that they are \"richly interconnected.\" They have interfaces and interact with each other. These interfaces and the reaction to changes of the shared variables are however clearly predefined. 2. Autonomy--Agents are not centrally controlled; they have a degree of autonomy but their behavior is always subject to certain laws, rules or norms. This criterion is not fulfilled. All subsystems have a predefined behavior that is centrally controlled. There is a typically a central control system (SCADA--supervisory control and data acquisition) which access all the inputs from all subsystems, provides control decision and affects the actuators/outputs. 3. Emergence--_Global behavior of a complex system emerges from the interaction of agents and, in turn, constrains agent behavior. Emergent behavior is unpredictable but not random._  
The emergence in behavior of a complex system is its crucial characteristic. Based on the behavior of partial agents, one cannot determine the overall behavior of the system. This is clearly not true for existing road tunnels. Here, the administration expects clear and predictable behavior. Without that, a road tunnel would not be put into operation. 4. Nonequilibrium--_Complex systems generate unpredictable disruptive events_. Similarly to the previous criterion, the purpose of tunnel control system is to avoid disruptive events. Even in case of a traffic accident, there are predefined rules that are addressing such situation. The objective is to minimize any disruptiveness. 5. Nonlinearity--_Relations between agents are nonlinear._  
This criterion is fulfilled as for example interaction between traffic parameters and environmental characteristics are nonlinear. This is true for most of the partial subsystems. 6. Self-Organization--_Complex systems self-organize, i.e., autonomously change their behavior or modify their structure, to eliminate or reduce impact of disruptive events (adaptability) or to repel attacks (resilience)._  
Tunnel systems do not self-organize. In order to ensure predictability (again, this is a characteristic expected by the road administrators), the behavior even in case of for example traffic accident is predefined. 7. Co-Evolution--_If we define the system environment as the set of all systems with which the system interacts, then we can postulate that complex systems are open, they adapt to their environments and, in turn, change their environments._  
As by self-organization, the existing control systems do not adapt to their environment. They can (and should) be adapted to the changes in environment by the system designers, but it is not a default property of the system. The arguments above showed that we cannot address road tunnel system as a \"complex system\" according to the system theory.