This paper discusses the need for bidirectional coupling between network simulation and road traffic microsimulation to evaluate Inter-Vehicle Communication (IVC) protocols more accurately. The authors developed a hybrid simulation framework called Veins, which combines the network simulator OMNeT++ and the road traffic simulator SUMO. This framework allows for dynamic interaction between the two simulators, enabling the simulation of how IVC protocols influence road traffic and vice versa. The paper presents a proof-of-concept study using two IVC protocols: a centralized Traffic Information System (TIS) with a preinstalled infrastructure and standard MANET routing, and a decentralized TIS without infrastructure using UDP-based broadcasting. The evaluation is conducted in a simple Manhattan Grid scenario and a more realistic environment using real street maps of Erlangen, Germany. The results demonstrate that bidirectional coupling significantly improves the realism of IVC evaluations, providing deeper insights into the impact of IVC on road traffic and vice versa. The framework also allows for the integration of environmental impact measures, such as CO2 emissions, to assess the overall effectiveness of IVC protocols. The authors conclude that bidirectional coupling is essential for realistic evaluations of IVC protocols and provides a more accurate means to assess their performance and environmental impact.This paper discusses the need for bidirectional coupling between network simulation and road traffic microsimulation to evaluate Inter-Vehicle Communication (IVC) protocols more accurately. The authors developed a hybrid simulation framework called Veins, which combines the network simulator OMNeT++ and the road traffic simulator SUMO. This framework allows for dynamic interaction between the two simulators, enabling the simulation of how IVC protocols influence road traffic and vice versa. The paper presents a proof-of-concept study using two IVC protocols: a centralized Traffic Information System (TIS) with a preinstalled infrastructure and standard MANET routing, and a decentralized TIS without infrastructure using UDP-based broadcasting. The evaluation is conducted in a simple Manhattan Grid scenario and a more realistic environment using real street maps of Erlangen, Germany. The results demonstrate that bidirectional coupling significantly improves the realism of IVC evaluations, providing deeper insights into the impact of IVC on road traffic and vice versa. The framework also allows for the integration of environmental impact measures, such as CO2 emissions, to assess the overall effectiveness of IVC protocols. The authors conclude that bidirectional coupling is essential for realistic evaluations of IVC protocols and provides a more accurate means to assess their performance and environmental impact.