Multi-shot Solving and Domain Heuristics for CASP-based Traffic Signal Optimisation

Traffic signal optimisation is a key approach to urban traffic control and aims to mitigate congestion in urban areas by adjusting the green‑light durations of traffic signals. While prior work has shown the viability of Constraint Answer Set Programming (CASP) for this task, specifically with the system clingcon, limitations remain in terms of scalability and solution quality. In this paper, we extend the existing CASP-based approach by incorporating multi‑shot solving to enable incremental reasoning, together with two domain‑specific heuristics designed to guide the search more effectively towards high‑quality solutions. We evaluate our approach on real-world benchmark instances, including more challenging settings that were not addressed in previous work. Overall, our enhancements represent a substantial advancement over the previous clingcon encoding, both in terms of coverage and solution quality, and compares favourably to PDDL+ methods.

Citation: Doria, F.; Ramagnano, G.; Tarzariol, A.; Maratea, M.; and Vallati, M. (2026). "Multi-shot Solving and Domain Heuristics for CASP-based Traffic Signal Optimisation". In Proceedings of the 18th International Conference on Logic Programming and Non-monotonic Reasoning, (LPNMR 2026), (To Appear).