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Providing real-time road traffic information to drivers is a critical step to improve road traffic efficiency by allowing appropriate routes to be chosen. In a Vehicular Ad hoc Network (VANET), a query message can be disseminated along several road paths for collecting road traffic information. While several VANET protocols have been proposed to accomplish such task, they were evaluated in different settings, environments, and a limited scale. To gain better insights for actual deployment, it is necessary to explore their relative performance advantages and limitations. In this paper, we compare Slotted 1-persistence, Efficient Directional Broadcast (EDB), Data dissemination pRotocol In VEhicular networks (DRIVE), and Road Traffic Collecting (RTC) protocols under a large scale city networks, high vehicle density, multiple query sessions, and the presence of interfering background traffic. The evaluation focuses on the average percentage of targeted road segment coverage, the total number of transmitted messages, and the completion delay time. The results show that EDB outperforms other protocols in terms of the road segment coverage with highest number of transmitted messages while RTC yields a lower number of transmitted messages with less road segment coverage. However, EDB requires road-side units at every intersection and its performance dramatically drops under the failure of road-side units.
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