CorridorLight: Cooperation as Task Negotiation with Causal Gating for Traffic Signal Control

Network-level traffic signal control (TSC) involves coordination under partial observability and strict real-time constraints. In real-world urban networks with dozens or hundreds of intersections, direct coordination incurs an intractably large joint action space, making centralized cooperation difficult to deploy in practice. We propose CorridorLight, which tackles this challenge by casting cooperation as task negotiation. A high-level Corridor Agent represents the network as a direction-level graph and periodically generates a small set of junction-disjoint corridor tasks via a seed-and-grow procedure. These tasks provide lane-level preference guidance, while Intersection Agents maintain fast decentralized control and selectively support the active corridor task. By learning when to cooperate versus act selfishly, CorridorLight enables an adaptive trade-off between local delay minimization and corridor-level relief, leading to improved global performance. To this end, we derive a closed-form, Lipschitz-continuous gating function by maximizing a counterfactual net gain between cooperative and selfish behavior, yielding smooth, interpretable cooperation without brittle heuristics. Experiments on synthetic grids and real-world networks show consistent system-level improvements and outperform cooperative TSC baselines across diverse topologies and demand patterns.