# BIM-Based Description of Intelligent Transportation Systems for Roads
## 2 Knowledge Sources for Semantic Modeling of ITS
### ITS Intelligent Infrastructure  
The facilities underlying road intelligent transportation systems enable sensing of the vehicular environment, supporting physical and computational processes, and controlling ITS applications. Therefore, it is vital to determine ITS infrastructure capabilities and resources to be reflected in the semantic model. ITS infrastructure is composed of (i) physical and spatial structural elements, i.e., road infrastructure, as well as (ii) a set of functional elements that together build the ITS architecture, the latter hereinafter termed \"ITS stations\".  
Regarding road intelligent transportation systems, ITS stations, whether fixed or mobile, are the core elements that add intelligence to roads. ITS stations, according to [47], may further be categorized into the following:  
* _Vehicle ITS stations (mobile)_, i.e., vehicular cyber-physical systems that comprise all vehicle types in vehicular environments, e.g., cars, trucks, and motorbikes;
* _Roadside ITS stations (fixed)_ that represent traffic shields and cameras, poles, and gantries;
* _Personal ITS stations (mobile)_, i.e., smart devices, such as cellphones and tablets; and
* _Central ITS stations (fixed)_, also known as \"control centers\".  
Different technologies enable ITS stations to interact with the vehicular environment. Regardless of underlying technologies, ITS stations are equipped with four main on-board resources, (i) sensing unit, (ii) computing unit, (iii) communication unit, and (iv) power unit. The sensing unit implements sensor networks and technologies, such as traffic detection systems and environmental-changes detectors. Micro-electro-mechanical systems (MEMS), inductive loops, radio-frequency identification (RFID), light detection and ranging (LiDAR) sensors, and automatic license plate recognition cameras are widely used components of traffic detection systems. Wheel speed sensors, rear object laser radars, and blind spot detection sensors are part of on-board sensing units in vehicle ITS stations. The main processing board and storage device that controls the computational processes constitute the computing unit. Communication devices, e.g., beacons, transceivers and routers, are represented by the communication unit, while the power unit comprises power-supply means, e.g., photovoltaic panels, piezoelectric transducers, or the electrical grid. In addition to the four main units, dedicated ITS stations may include actuating and control devices to comply with traffic and safety demands, to prevent hazardous situations, or to change the behavior of ITS stations.  
Summarizing the information stated above, ITS stations are decent candidates for describing ITS intelligent infrastructure on a technology-independent semantic basis. Therefore, in this paper, ITS intelligent infrastructure is reflected in the semantic model in terms of vehicle, roadside, personal, and central ITS stations with on-board sensing, computing, communication, and power units. In the following subsection, connections between ITS station on-board resources, as well as communications between ITS stations that facilitate data sharing process, are shown.