<p>This study investigates the platoon formation problem for autonomous trucks, in which vehicles accumulate at a staging station prior to entering the highway. Although platooning reduces aerodynamic drag and improves fuel efficiency—with larger platoons providing greater energy savings—it also increases inter-departure intervals, potentially compromising service frequency and schedule reliability. To address this trade-off, we analyze a dual-threshold (<i>T</i>, <i>N</i>) policy: a platoon departs either when the maximum waiting time <i>T</i> since the first vehicle’s arrival is reached, or when the number of waiting vehicles reaches the target size <i>N</i>. We derive explicit expressions for the resulting platoon size, waiting time, and inter-departure intervals, as well as the expected per-vehicle energy consumption. Numerical experiments under diverse traffic scenarios demonstrate that the (<i>T</i>, <i>N</i>) policy achieves significant energy savings while ensuring operational stability through controlled departure intervals. These results indicate that the (<i>T</i>, <i>N</i>) policy offers a robust and practical framework for the early deployment of autonomous truck platooning systems.</p>