Vehicle-to-vehicle (V2V) and vehicle-to-roadside (V2R) communications is required for numerous applications that aim at improving traffic safety and traffic efficiency. As recent studies have shown, communications in this context is significantly influenced by radio propagation characteristics of the environment and the signal processing algorithms that are executed on the physical layer of the communications stack. Whereas a shadowing of the transmitted signal, e.g. due to buildings, determines the ability to communicate around corners, channel estimation, channel equalizing, and advanced coding schemes determine whether a receiver can decode a received signal succesfully or not. Consequently, a proper assessment and evaluation of V2V and V2R communications, especially when traffic safety applications are considered, requires an accurate simulation of the wireless channel as well as the physical layer of the protocol stack. To enable a proper assessment, we integrated a physical layer simulator into the popular NS-3 network simulator, validated our implementation against commercial off the shelf transceiver chipsets, and employed ray tracing as a method to accurately simulate the radio propagation characteristics of the Karlsruhe Oststadt. ... mehrSince the simulation of signal processing details and ray tracing are computationally expensive modeling methods, we based our work on the HP XC4000 to speedup the computation of both aspects.