## 2 Background
### The Simulation Context  
The first ITS-G5-based C-ITS pilot in Hungary was implemented in 2015 along a 136 km-long stretch of the motorway M1 between Vienna and Budapest. The ITS-G5 technology supports vehicle-to-vehicle, vehicle-to-everything ad hoc communications without prior network set-up used at the dedicated 5.9 GHz frequency bands in Europe (the specified access layer of the communication stack is collectively called ITS-G5). The trial focused on road safety, especially on work zone use cases. Therefore, maintenance vehicles were also equipped with transceivers to act like ad hoc roadside units besides the fixed R-ITS-S stations. They were capable of operating both in connected and in standalone mode. By using an additional switch connected to the installed OBU, the operator can easily generate a DENM message which is broadcasted at the spot directly (standalone mode) or via the central ITS station (connected mode). The C-Roads Platform [43] is considered \begin{table}
\begin{tabular}{l l l} \hline \hline
**Use Case** & **Generation** & **References** \\ \hline Forward collision & Day1, Day2 & [12; 13; 14] \\ Intersection collision & Day1, Day2 & [15; 16] \\ Speed advisory & Day1 & [17] \\ Adverse weather & Day1 & [18; 19] \\ Dangerous situation & Day1, Day2 & [20; 21; 22; 23] \\ Special vehicle & Day1 & [24; 25; 26] \\ Stationary vehicle & Day1 & [27] \\ Green light optimal speed advisory & Day1 & [28; 29; 30] \\ Red light violation & Day1 & [31] \\ VRU protection & Day2 & [32] \\ Collective perception & Day2 & [18; 33; 34; 35; 36; 37] \\ Cooperative awareness & Day1 & [38; 39] \\ Maneuver Coordination & Day3 & [40; 41; 42] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: C-ITS use cases evolution. an adequate instrument for Member States to continue their involvement in the dynamic field of C-ITS and to delve into more detail from a particular road operator perspective. Member States across Europe are installing C-ITS pilot sites needed for the testing and later operation of \"Day1\" and beyond recommended by the European Commission's \"C-ITS platform\". Therefore, Member States will invest in their infrastructure; OEMs and the industry will use that pilot test infrastructure to test components and services. As part of C-Roads, Hungarian Public Roads upgraded and extended the 2015 pilot in coverage and functionality. Additional Day1 use cases were introduced with hybrid communication along Motorway M1 (toward Austria) and Motorway M7 (toward Croatia and Slovenia). The provided services/the names of their sub-cases are as follows: IVS-DSLI, IVS-EVFT, IVSDLM, IVS-OSI, HLN-AZ, HLN-TJA, HLN-WCW, HLNTSR, HLN-OR, RWW-LC, RWW-RC, and RWW-RM (as in C-ROADS Harmonized Communication Profiles Rel. 1.6). In addition to core network corridors, special attention was also paid to urban applications: traffic light controllers were improved in the town of Gyor to provide Time To Green and Green Light Optimum Speed Advisory (SI-GLOSA/SI-SPTI) information and Intersection Violation Warning (SI-ISVW) at ten neighboring junctions along the main traffic route, where intersection safety services are also available. The pilot sites have been operational since Q1 2021 [44]. Based on the C-Roads Platform results, the parallel CROCODILE project [45] Phase 2 also aimed for new C-ITS investments, mainly focusing on the Budapest Ring Road (expressway M0), implementing a testbed of cooperative ITS functions for the Central Region of Hungary (concerning the plan of the national C-ITS infrastructure). The deployment was started before the C-Roads investments, but the work strongly relied on the outcomes. Therefore, all the installed 26 Road Side Units (RSUs) at 13 locations (see Figure 1 for details) comply with the then-available C-Roads technical specs (\"C-ROADS--Harmonized C-ITS Specifications for Europe--Release 1.3\"). As a result of the investment, Commsignia ITS-RS4-M transceivers [46] provide ITS-G5 communication links at least every 10 km along the M0 ring road around Budapest (in both directions).