This paper presents a hybrid simulation framework called Veins, which combines network simulation (OMNeT++) and road traffic microsimulation (SUMO) for evaluating Inter-Vehicle Communication (IVC) protocols in Vehicular Ad Hoc Networks (VANETs). The framework enables bidirectional coupling between network and road traffic simulations, allowing for more realistic evaluation of IVC protocols. The need for such coupling arises from the fact that the selection of a mobility model significantly affects simulation outcomes, and the use of a representative model is essential for meaningful evaluations. Veins integrates these two simulation tools to provide dynamic interaction between them, enabling the network simulation to control the road traffic simulation and vice versa. This bidirectional coupling allows for the simulation of the influence of VANET communications on road traffic and the provision of information from road traffic simulations to the network simulation. The framework also includes a model for CO₂ emissions of cars to support environmental impact studies. The paper demonstrates the advantages of bidirectional coupling through a proof-of-concept study evaluating two IVC protocols for incident warning over VANETs. The results show that bidirectional coupling provides more accurate and realistic evaluations of IVC protocols compared to traditional trace-driven simulations. The study also highlights the importance of considering environmental impact when evaluating IVC protocols. The paper concludes that bidirectional coupling of network and road traffic simulations is essential for evaluating IVC protocols in VANETs, as it allows for more accurate and realistic evaluations of protocol performance and environmental impact.This paper presents a hybrid simulation framework called Veins, which combines network simulation (OMNeT++) and road traffic microsimulation (SUMO) for evaluating Inter-Vehicle Communication (IVC) protocols in Vehicular Ad Hoc Networks (VANETs). The framework enables bidirectional coupling between network and road traffic simulations, allowing for more realistic evaluation of IVC protocols. The need for such coupling arises from the fact that the selection of a mobility model significantly affects simulation outcomes, and the use of a representative model is essential for meaningful evaluations. Veins integrates these two simulation tools to provide dynamic interaction between them, enabling the network simulation to control the road traffic simulation and vice versa. This bidirectional coupling allows for the simulation of the influence of VANET communications on road traffic and the provision of information from road traffic simulations to the network simulation. The framework also includes a model for CO₂ emissions of cars to support environmental impact studies. The paper demonstrates the advantages of bidirectional coupling through a proof-of-concept study evaluating two IVC protocols for incident warning over VANETs. The results show that bidirectional coupling provides more accurate and realistic evaluations of IVC protocols compared to traditional trace-driven simulations. The study also highlights the importance of considering environmental impact when evaluating IVC protocols. The paper concludes that bidirectional coupling of network and road traffic simulations is essential for evaluating IVC protocols in VANETs, as it allows for more accurate and realistic evaluations of protocol performance and environmental impact.