Overview of Service Request #2: Why Is This Red Light So Damn Long?
This episode of Service Request (99% Invisible) investigates why traffic lights in Los Angeles feel interminably long. Through a mix of on-the-ground reporting and interviews with traffic engineers, the show traces the origins and workings of LA’s centralized signal system (ATSAC), explains the tech and trade-offs behind signal timing, and illustrates why some intersections—no matter how smart—remain persistently awful.
Key takeaways
- LA’s centralized traffic-control system (ATSAC) grew from an emergency project for the 1984 Olympics into a citywide operation managing nearly 5,000 signals.
- Sensors embedded in pavement and cameras feed real-time data to a downtown control room where algorithms and engineers adjust signal timing to reduce delay and stops.
- Signal timing can and does improve traffic flow, but it can’t change city layout or the fundamental problem of too many vehicles for fixed road space.
- Traffic engineering is “managing in space and time”: engineers can’t add space, so they manipulate time (light cycles) and accept trade-offs—prioritizing higher-volume corridors at the expense of side streets.
- Some intersections—like the Fairfax/Olympic/San Vicente “Fairfax asterisk” (aka the Devil’s Three‑Way)—are geometrically messy and likely to remain problematic despite advanced controls.
How LA’s traffic system (ATSAC) works
- Origin: Built as an experiment to handle Olympic traffic in 1984 (led by Ed Rowe); it connected many nearby signals so engineers could adjust timing remotely.
- Scale: Now called ATSAC (Advanced Transportation System and Coordination); controls nearly 5,000 traffic signals across the city.
- Sensors & data: Inductive sensors buried in pavement count cars and measure speed/density; hundreds of cameras provide visual context.
- Communications: Sensor and camera data travel via underground fiber to a central control room.
- Automation + humans:
- Algorithms continuously adjust green times, cycle lengths, and coordination to reduce delay and stops.
- Human operators in the control room monitor maps and video, intervene during crashes, sinkholes, protests, or other unusual events, and can manually override signals in emergencies.
- Measured benefits cited: during the original Olympic rollout delay fell ~30–35%; later improvements cited reductions in stops (~35%) and delay (~20%) in some contexts.
Trade-offs, limitations, and design reality
- Space vs. time: Streets are finite; engineers can’t create more road space, so they allocate time (who gets green) to maximize throughput.
- Utilitarian choices: Systems prioritize the routes carrying the most people/vehicles (main arterials) even if that means extra wait for side streets.
- Human behavior matters: Small pavement and marking changes alter driving behavior; traffic engineering blends math with behavioral “art.”
- Irreducible problems: Some intersections’ geometry and historic street layouts create bottlenecks that timing software can’t fully fix (the Fairfax asterisk is a clear example).
Story highlights & anecdotes
- On-the-ground framing: Reporters and producers get stuck at the Fairfax asterisk and use that frustration to probe the system’s limits.
- Control room imagery: ATSAC’s downtown operations center is described like “mission control” with massive screens showing signal status and live camera feeds; it’s been dramatized in films (e.g., The Italian Job).
- Notable line: Traffic engineers describe their work as “managing movement through a city… in space and time,” capturing the core constraint they face.
Who’s interviewed / credited
- Salita (Salida) Reynolds — Chief Innovation Officer at LA Metro; ran LA’s traffic light system for eight years.
- Eric Zambon — Transportation engineer in charge of the ATSAC center for LADOT.
- Producer Vivian Lay and her husband Cody Franklin appear in field reporting.
- Historic reference and archival voices include Ed Rowe (ATSAC founder; died 2023).
What this means for drivers
- When you sit at a long red light, it’s often the result of deliberate trade-offs meant to move the most people most efficiently across the network—not just local indifference.
- Some intersections will remain persistently bad because of street geometry and demand; smarter signals help, but they’re not a panacea.
- The ATSAC system will continue evolving (ATSAC 3.0) and is expected to play a central role in managing traffic for future large events like the 2028 Olympics, including better coordination for transit, bikes, and pedestrians.
Resources & next steps
- To submit a question to the podcast: servicerequest@99pi.org (for show topic requests).
- For broader context on urban traffic systems: look for coverage of ATSAC, adaptive signal control systems, and city transportation planning practices.
- If you want to follow the show: 99% Invisible episodes and credits are referenced in the episode wrap-up.
Bottom line
LA’s traffic lights are the product of decades of technical innovation and difficult choices. ATSAC has measurably improved flow across thousands of intersections, but it must constantly balance competing uses of fixed space—so sometimes a red light feels long because the system is prioritizing the greatest good for the greatest number, and sometimes the street itself is simply poorly designed for modern traffic volumes.