When better traffic forecasts fail to improve signal control: a layered diagnostic study of forecast-to-decision value
This study investigates why improved traffic prediction fails to enhance signal control performance, focusing on the "value gap" between prediction and decision-making. We propose a hierarchical diagnostic framework and a practical auditing protocol, leveraging real-world data from Xuancheng within a closed-loop controller setting. By integrating conformal intervals, dependence-aware scenario generation, causal prediction, and exhaustive joint action search, we systematically evaluate how prediction accuracy, uncertainty quantification, and interface alignment affect control outcomes. Our findings reveal a counterintuitive phenomenon wherein reduced prediction errors paradoxically increase queue lengths. Furthermore, this work establishes the critical roles of temporal observability, action identifiability, and objective alignment, offering a precise diagnostic methodology for identifying cross-stage failures in prediction-driven traffic control systems.