GrooveNet is a hybrid simulator which enables communication between simulated vehicles, real vehicles and between real and simulated vehicles. By modeling inter-vehicular communication within a real street map-based topography it facilitates protocol design and also in-vehicle deployment. GrooveNet’s modular architecture incorporates mobility, trip and message broadcast models over a variety of link and physical layer communication models. It is easy to run simulations of thousands of vehicles in any US city and to add new models for networking, security, applications and vehicle interaction. GrooveNet supports multiple network interfaces, GPS and events triggered from the vehicle’s on-board computer. Through simulation, we are able to study the message latency, and coverage under various traffic conditions. On-road tests over 400 miles lend insight to required market penetration.