The critical step in deploying a V2R system based on digital broadcast systems such as DAB or DVB-H is the estimation of its downlink capacity requirements. We present an entropy based model for the downlink capacity requirements that takes into consideration both the parameters of the fixed infrastructure of the V2R system, as well as the dynamic traffic conditions. This model is independent of the encoding and compression methods used. The results of applying the model to one regional and one nation-wide V2R system, both under normal and heavy traffic scenarios, are also presented. We show how these results can be used to parameterize any chosen digital broadcast system, in order to meet the requirements of the V2R system while minimizing the rollout and operational costs.