Many vehicular ad hoc applications rely on vehicular broadcasting-based multi-hop routing to disseminate messages. In this work, we study the question of vehicular broadcasting-based routing. In particular, by modelling the vehicular message dissemination with a limited-time epidemic dynamics, we propose an online self-adaptive beaconing method to dynamically learn the optimal beaconing policy for vehicular broadcasting with consideration of varying opportunistic contacts between vehicles. The vehicular broadcasting incorporated within the proposed method can ensure message delivery with low dissemination delay and routing cost. Both theoretical analysis and simulation results are provided to exhibit the robustness and effectiveness of the proposed solution and the significantly performance with respect to the conventional solution.