---
title: >-
  City of Pittsburgh and Carnegie Mellon University: SURTRAC decentralized adaptive
  traffic-signal control
slug: pittsburgh-surtrac-signals
stable_id: caa36ddc69a55deb
company: City of Pittsburgh and Carnegie Mellon University
function_code: engineering
pattern_codes:
  - coordination_compression
  - continuous_decisioning
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.
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
---

# City of Pittsburgh and Carnegie Mellon University: SURTRAC decentralized adaptive traffic-signal control

That urban intersections should follow fixed timing plans optimized offline for predictable rush periods.

Function: Engineering design. Patterns: Coordination compression; Continuous decisioning. Evidence: verified.

Freshness: current. Reviewed: 2026-08-23. Updated: 2026-08-22.


Source quality: 1 independent, 1 peer reviewed; publication outcomes are verified.

## Before

1. **Traffic engineers** — Create fixed coordinated timing plans for rush periods and simple actuated control otherwise. (control: Offline plans)
2. **Signal controller** — Apply the preset phase plan until engineers update it. (control: Static schedule)

## After

1. **SURTRAC agent at each intersection** — Recomputes green-time allocation every one to two seconds from incoming flows. (control: Safety and phase constraints)
2. **Intersection agents** — Share projected outflows with neighboring signals to form coordinated corridors. (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.

## Outcomes

- **Average travel time and wait time** (verified): Coordinated fixed plans and simple actuated control in March 2012 before testing → 25.79% lower travel time and 40.64% lower wait time; projected emissions 21.48% lower. Before/after drive-through study, not randomization; emissions were modeled from fuel use rather than directly measured.

## 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?

## Sources

- [Smart Urban Signal Networks: Initial Application of the SURTRAC Adaptive Traffic Signal Control System](https://doi.org/10.1609/icaps.v23i1.13594) — ICAPS
- [A decentralized signal system pilot showed overall improvements](https://www.itskrs.its.dot.gov/2013-b00820) — U.S. Department of Transportation ITS Deployment Evaluation