{"stable_id":"caa36ddc69a55deb","slug":"pittsburgh-surtrac-signals","company":"City of Pittsburgh and Carnegie Mellon University","workflow_name":"SURTRAC decentralized adaptive traffic-signal control","function_code":"engineering","pattern_codes":["coordination_compression","continuous_decisioning"],"changed_assumption":"That urban intersections should follow fixed timing plans optimized offline for predictable rush periods.","evidence_strength":"verified","publication_tier":"showcase","freshness":"current","reviewed_at":"2026-08-23","updated_at":"2026-08-22","source_quality_summary":"1 independent, 1 peer reviewed; publication outcomes are verified.","caveat_summary":"Before/after drive-through study, not randomization; emissions were modeled from fuel use rather than directly measured.","freshness_caveat":null,"workflow_summary":{"before":[{"actor":"Traffic engineers","action":"Create fixed coordinated timing plans for rush periods and simple actuated control otherwise.","actor_type":"control"},{"actor":"Signal controller","action":"Apply the preset phase plan until engineers update it.","actor_type":"control"}],"hinge":"That urban intersections should follow fixed timing plans optimized offline for predictable rush periods.","after":[{"actor":"SURTRAC agent at each intersection","action":"Recomputes green-time allocation every one to two seconds from incoming flows.","actor_type":"ai"},{"actor":"Intersection agents","action":"Share projected outflows with neighboring signals to form coordinated corridors.","actor_type":"system"}],"decision_mode":"retained","decision_marker":"Human authority remains at the consequential boundary"},"before":[{"order":1,"actor":"Traffic engineers","action":"Create fixed coordinated timing plans for rush periods and simple actuated control otherwise.","handoff_to":"Signal controllers","control":"Offline plans"},{"order":2,"actor":"Signal controller","action":"Apply the preset phase plan until engineers update it.","handoff_to":"Road users","control":"Static schedule"}],"after":[{"order":1,"actor":"SURTRAC agent at each intersection","action":"Recomputes green-time allocation every one to two seconds from incoming flows.","handoff_to":"Local signal controller","control":"Safety and phase constraints"},{"order":2,"actor":"Intersection agents","action":"Share projected outflows with neighboring signals to form coordinated corridors.","handoff_to":"Adjacent intersections","control":"Decentralized coordination"}],"decision_rights":"Intersection agents allocate routine green time within traffic-safety constraints; public authorities retain configuration and shutdown rights.","exception_path":"Engineers and conventional controller modes handle sensor, communication, emergency, and system failures.","removed_work":["Repeated manual retiming for normal traffic variation","Waiting caused by fixed plans that do not match current flow"],"outcomes":[{"metric":"Average travel time and wait time","baseline":"Coordinated fixed plans and simple actuated control in March 2012 before testing","result":"25.79% lower travel time and 40.64% lower wait time; projected emissions 21.48% lower","period":"Before/after field runs in March and June 2012","scale":"Twelve high-volume routes through nine intersections, nearly 30,000 weekday vehicles","attribution_caveat":"Before/after drive-through study, not randomization; emissions were modeled from fuel use rather than directly measured.","evidence_label":"verified"}],"executive_lesson":"The system made a high-frequency physical decision locally while coordinating only the information needed across neighbors.","anti_pattern":"Reporting modeled emissions as direct measurement or deploying without safe fallback timing.","questions_for_leaders":["Which decisions need central control versus local agents?","What happens when sensing fails?"],"collections":["human-still-decides","queue-eliminated","embodied-work"],"bundle_version":"1.0.0","bundle_fingerprint":"sha256:c23c6cc2b88153d008ea8fda928f632ce0011fc2d4c5036672a16e5d895bab93","canonical_url":"https://brianletort.ai/transformations/pittsburgh-surtrac-signals"}