This paper proposes a model to calculate the average speed of transmission of intervehicle communication (IVC) messages in a general traffic stream on highways in the early stage of deploying distributed traffic information systems (DTIS). The model helps explain the relationship between average IVC message speed and traffic parameters such as equipped vehicle density, traffic flow speed, and traffic direction. Simulation results are used to verify the correctness of the model. This model needs a much shorter calculation time than a simulation. Moreover, the theoretical analysis helps provide more insightful explanations of the phenomenon for IVC performance analysis. The results of this paper would help people better understand the design criteria for DTIS.