Service Request #2: Why Is This Red Light So Damn Long? - 99% Invisible Recap

Podcast: 99% Invisible

Published: 2026-03-24

Duration: 1681

Guests: Salita Reynolds, Eric Zambon, Vivian Lay

What Happened

Los Angeles has long been synonymous with traffic congestion, a reputation that dates back to its modern traffic system roots established during the 1984 Olympic Games. During this period, the city integrated 118 traffic lights into a single system to effectively manage the increased traffic. This system reduced delays by approximately 30-35% and improved emissions, setting a precedent for traffic management.

The Advanced Transportation System and Coordination (ATSAC) now manages nearly all of LA's 5,000 traffic signals, making it the world's most advanced traffic system. Sensors embedded in the pavement at intersections send data back to a control room, enabling real-time traffic light adjustments. This control room functions similarly to NASA's Mission Control, with engineers monitoring traffic through hundreds of cameras.

Despite its sophistication, the ATSAC system faces challenges such as the Fairfax intersection, where Fairfax, Olympic, and San Vicente meet. This complex intersection, known as the Fairfax asterisk, exemplifies situations where signal timing cannot solely resolve traffic issues. Balancing traffic flow at such intersections is an art that involves considering human behavior and the quality of urban life.

Eric Zambon, a Transportation Engineer in charge of the ATSAC Traffic Management Center for LA DOT, explains that the system uses algorithms to manage traffic flow based on data like rush hour patterns and holiday surges. The goal is to prioritize major routes with higher traffic volumes while balancing space and time.

The ATSAC system serves as a model for other cities, although many municipalities only have partial traffic management systems. With the upcoming 2028 Olympics in Los Angeles, the city plans to expand and enhance this system further to accommodate the anticipated surge in traffic.

Salita Reynolds, Chief Innovation Officer at LA Metro, and Vivian Lay, Supervising Producer at 99% Invisible, discuss the broader implications of LA's traffic management system. They highlight its significance in setting a standard for urban traffic systems worldwide, emphasizing the blend of technology and human-centric design.

Key Insights

• Los Angeles's traffic system, ATSAC, controls nearly all of the city's 5,000 traffic signals, making it the world's most advanced. It originated from the 1984 Olympics, which led to the integration of 118 traffic lights into a unified system to manage increased traffic.
• The ATSAC control room operates like NASA's Mission Control, using sensors and cameras to make real-time adjustments to traffic lights. This system reduces delays by 30-35% and improves emissions by optimizing traffic flow.
• Complex intersections like the Fairfax asterisk present unique challenges that signal timing alone cannot resolve. Traffic engineering in these areas requires a balance between space, time, and human behavior.
• With the 2028 Olympics approaching, Los Angeles plans to further develop the ATSAC system to handle the additional traffic. This expansion aims to maintain LA's status as a model for urban traffic management systems.