# Congestion-Free Ant Traffic: Jam Absorption Mechanism in Multiple Platoons
## 5 Analysis of Jam-Free Ant Traffic
### Inter-Platoon Analysis  
Contrary to the previous perception, the intra-platoon analysis presented above showed no synchronization between ants in a platoon. Furthermore, evidence of stop-and-go motion was found due to queuing. Therefore, to understand AT systems in more detail, we analyzed inter-platoon relationships. For the inter-platoon analysis, we selected a pair of adjacent platoons that we referred to as the leading platoon and the following platoon, considering the direction of travel. We simulated the heterogeneous scenario described in the intra-platoon analysis. We selected a pair of platoons that were separated by a sufficient distance to ensure that they would not merge into each other in the free-flow phase. We analyzed an intersection of two adjoining platoons, which included (1) an analysis of the last ant in the leading platoon, (2) an analysis of the space in between the two platoons (i.e., the headway of the following platoon), and (3) an analysis of the first ant in the following platoon. We conducted the above-mentioned analysis by observing the data of the last ant in the leading platoon and the first ant in the following platoon.  
Prototypical results of the inter-platoon analysis of the free-flow phase are shown in Figure 7, where (a) the velocity-position relationships and (b) the space-time relationships for the last ant in the leading platoon and the first ant in the following platoon are compared. As shown in Figure 7a, although the velocity of the last ant in the leading platoon decreased well before the bottleneck (for the reason given in the intra-platoon analysis above), the velocity of the leader of the following platoon decreased suddenly at the bottleneck. At the same time, concurring with the above observation, the upstream part of the bottleneck in Figure 7b also shows that although the inter-platoon distance decreased, it did not decrease enough to force the leader of the following platoon to reduce its velocity. This means that the velocity of the leader of the following platoon was independent of the velocity of the last ant in the leading platoon, and stop-and-go motion due to queuing in the leading platoon did not affect the following platoon. This phenomenon can be explained by jam-absorbing driving in [30; 31]. In jam-absorption driving from [30; 31], in response to a trigger of stop-and-go motion (e.g., sudden braking), the following driver creates enough headway to avoid stop-and-go motion. In AT, the inter-platoon distance (referred to as the jam absorption buffer (JAB)) acts similarly to the above-mentioned headway of jam-absorbing driving. The JAB provides enough time for dissipation of the queuing effect due to the leading platoon. Thus, the leader of the following platoon does not get involved in stop-and go-motion due to the leading platoon. Furthermore, in Figure 7, it is interesting to note that at the downstream end of the bottleneck, the velocity of the last ant in the leading platoon rose earlier and was higher compared to the leader of the following platoon. This is where a JAB was created, indicating that a fast-out action created a JAB at the downstream end of a bottleneck, thereby helping to avoid stop-and-go motion at the upstream end. We also observed that for given densities in the free-flow phase, the leaders of all platoons in established traffic flow moved with the same \((v_{avg})\), which led to the same \(v_{avg}\) for all platoons. The similar \(v_{avg}\) in established traffic flow prohibited the platoon from converging. The above observation about non-convergence is contradictory to previous studies, which argued that platoons in AT have convergence behavior, which leads to the formation of a single platoon [5; 12; 14; 27].