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This paper presents a method for efficient exchanges of Data Elements between vehicles running multiple safety applications. To date, significant efforts have been made in designing lower-layer communication protocols for VANET. Also, industry and government agencies have made progress in identifying and implementing certain vehicular safety applications. However, the specific environment of VANETenabled safety applications lends itself to significant efficiencies in how information is coordinated within a vehicle and transmitted to neighboring vehicles. These efficiencies are instantiated in what we call the Message Dispatcher. The Message Dispatcher is an interface between multiple safety applications and the lower-layer communication stack. This Message Dispatcher concept was recently contributed to the Society of Automotive Engineers (SAE) and has become an underlying principle in their safety message standardization process. It has also been implemented in vehicle demonstrations at the Toyota Technical Center (TTC) in Ann Arbor, MI.

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Wireless intervehicular communication will enable a broad range of applications in the future. However, multiple vehicles, multiple diverse applications, multiple vehicle manufacturers, and the mobile vehicular environment raise several issues related to utilizing the wireless medium effectively. In this paper, we present a method for efficiently communicating vehicle data among neighboring vehicles, primarily for safety applications. The "Message Dispatcher" (MD) coordinates communication between applications and the wireless channel at the application level. It addresses technical implementation issues, business deployment considerations, and issues of extensibility and system architecture. The MD concept has become an integral part of the Society of Automotive Engineers' safety message-standardization effort. We shall describe the MD and present results illustrating its utility. We also describe a deployment in several vehicles at Toyota Technical Center in Ann Arbor, MI. Then, using data collected from the vehicles, we investigate a predictive-coding method for data transmission using the MD. We show that this scheme can reduce wireless-channel utilization and bandwidth requirements by over 80%, as compared to regular transmission methods. Several insights for future wireless-channel usage optimization are provided.