# Designing a C-ITS Communication Infrastructure for Traffic Signal Priority of Public Transport
### Motivation  
For some time now, the state of connected, cooperative, and intelligent transport systems (C-ITSs) has evolved, as the process through which these systems are developed shifted from theoretical research to practical testing until they were ready for area-wide deployment. As of today, the ITS is ready for the market and is gradually being rolled out in vehicles from well-known automobile manufacturers. The basic idea of an interaction between infrastructure components, such as the traffic light system (TL) and the vehicle, including the driver, is the continuous exchange of data and information in order to improve the quality of traffic flow and ultimately increase traffic safety. Due to the high potential that can be reached through cooperation, collaboration, and digitization, quite a few C-ITS services are currently being implemented, including their new characteristics for optimizing traffic control. The most common ITS service, TSP (Traffic Signal Priority), is currently the focus of international attention. This benefits all road users and traffic participants but is primarily intended to increase the effectiveness of public transport, e.g., in North America [2], Europe [3,4], and Asia [5]. Initially, the process of prioritization was individually examined. Today, the service is viewed as an integral part of mobility solutions. The full cycle/approach of cooperative services is realized by SRM messages, which are used to send data from vehicles to the infrastructure (V2I). To complete the communication cycle, the infrastructure then sends a response back to the vehicles using SSM messages. From this point on, the original ITS application becomes a C-ITS service. The optimization of traffic can subsequently be solved by the cooperation and adaptation of the TL control on the one hand and influencing the behavior of the vehicles, drivers, pedestrians, etc., on the other hand. In order to leverage all the potentials of C-ITS, new control mechanisms are necessary; these differ fundamentally from current procedures, for example, with regard to the ways in which local public transport is prioritized. In the near future, within the next few years, the predominantly widespread method of analog, mostly R09.xx data telegrams, will have to be replaced. The paradigm shift from today's static reporting procedure to linear recording using standardized C-ITS messages opens up completely new perspectives that must be taken into account, especially when considering the need to conform with regulatory bodies. The singular transmission of a vehicle's position via the registration points has reached its limits in terms of its capabilities, especially in the case of inconsistent traffic flow, such as traffic jams on individual access roads and intersections. In the future, linear and dynamic detection of vehicles entering a traffic light system via C-ITS will offer a significant improvement in potential. Even though analog radio frequencies for voice radio will no longer be awarded/granted from 2028 onward, the influence of the VDV (Verband Deutscher Verkehrsunternehmen, Association of German Transport Companies) on the German Federal Network Center has ensured that large parts of the analog radio frequencies for the prioritization of public transport can be retained until 2038. However, this requires a remapping of the 20 kHz frequency to a 12.5/25 kHz frequency from 2028 on. This form of remapping is currently possible with newer radio modules via a software update, yet the older devices may need to be replaced completely [6]. The VDV, however, has not yet received further assurance from the Federal Network Agency that the analog radio frequencies will be retained after 2038. Due to this technological shift, transportation and mobility providers as well as local authorities are currently working on replacing their procedures for the vehicle registration points, which have existed for 30 years, since C-ITS enables a new way of vehicle prioritization, specifically for public transportation.