<p>Spatio-temporal grid reservation has been studied as an efficient coordination framework for connected and automated driving, where each vehicle reserves its intended time and space through a dynamic map server. Although a previous study applied this framework to highway merging, it was evaluated in a simplified environment that did not consider lane changes on the mainline. In this study, we implement the spatio-temporal grid reservation framework on a dynamic-map–based system and extend the merging coordination mechanism to incorporate lane changes. By enabling mainline vehicles to change lanes in advance when the merge point is predicted to be occupied, the system leverages wide-area traffic information to alleviate congestion near the merging area. Simulation results show that this extension reduces travel time delay and decreases the frequency of sudden deceleration events, indicating improved efficiency and safety in highway merging coordination.</p>