The　death　toll　due　to　highway　crashes　is　increasing　at　an　alarming　rate　across　the　globe.　Vehicular　Ad　Hoc　Networks　(VANETs)　have　emerged　as　a　promising　solution　to　prevent　crashes　by　enabling　collision　avoidance　applications.　However,　a　robust　and　stable　collision　avoidance　application　is　a　cross-layer　problem　that　must　address　a　number　of　key　challenges　across　all　layers　of　a　VANET　communication　architecture.　This　paper　presents　and　evaluates　a　novel　VANET　protocol　suite,　named　Direction-Aware　Vehicular　Collision　Avoidance　(DVCA),　which　covers　application,　security　services,　network,　and　link　layers.　DVCA　is　a　vehicle-to-vehicle　communication　architecture　that　provides　enhanced　collision　probability　computation　and　adaptive　preventive　measures　for　cooperative　collision　avoidance　on　bi-directional　highways.　Moreover,　DVCA　enables　secure,　in-time,　and　reliable　dissemination　of　warning　messages,　which　provides　adequate　time　for　vehicles　to　prevent　collisions.　Simulation　and　analytical　results　demonstrate　reasonable　reduction　in　collisions　by　DVCA,　as　compared　with　eminent　VANET　communication　architectures.