We perform an extensive study of cooperative awareness in vehicular communication based on periodic message exchange. We start by analyzing measurements collected on four test sites across Europe. To measure cooperative awareness, we use three metrics: 1) neighborhood awareness ratio; 2) ratio of neighbors above range; and 3) packet delivery rate. Using the collected data, we define a simple model for calculating neighborhood awareness given packet delivery ratio for a given environment.

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... , we perform realistic, large-scale simulations to explore the achievable performance of cooperative awareness under realistic transmit power and transmit rate constraints. Our measurements and simulation results show that: i) above a certain threshold, there is little benefit in increasing cooperative message rate to improve the awareness; higher transmit power and fewer messages transmissions are a better approach, since message delivery is dominated by shadowing. ii) the efficacy of cooperative awareness varies greatly in different environments on both large scale (e.g., 90\% awareness is achievable up to 200~m in urban and over 500~m in highway) and small scale (e.g., vehicles in nearby streets can have significantly different awareness); iii) V2V and V2I communication have distinct awareness patterns; iv) each location has a distinct transmit power that achieves high awareness; and v) achieving high awareness levels results in increased reception of potentially unwanted messages; therefore, a balance needs to be found between awareness and interference, depending on the specific context. We hope our results will serve as a starting point for designing more effective periodic message exchange services for cooperative awareness.