In previous papers, the authors presented the link layer for a Communications Architecture for Reliable Adaptive Vehicular Adhoc Networks (CARAVAN), This robust space division multiplexing protocol mitigates the threat of a variety Denial of Service attacks on the inter-vehicle communication (IVC) network. However, this type of protocol tends to produce larger multi-hop message latencies than carrier sense link layer protocols, such as the one proposed in the Dedicated Short Range Communication (DSRC) IVC standards. This paper presents physical layer specification and network layer protocol for CARAVAN, which address this drawback. The physical layer is split into two frequency bands with radio ranges that are selected based on the requirements of the messages carried in each band. The network protocol includes message forwarding rules and a method that leverages the benefits of varying radio ranges to speed delivery of a-periodic messages. The results of simulation studies demonstrate that with these new features, CARAVAN produces message propagation latencies that are analogous to or better than less secure, currently proposed IVC protocols.