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99% Invisible

Service Request #2: Why Is This Red Light So Damn Long?

March 24, 2026 • 28m

Summary

⏱️ 7 min read

Overview

This episode explores how Los Angeles manages its notorious traffic through ATSAC (Advanced Transportation System and Coordination), a sophisticated network that controls nearly 5,000 traffic signals across the city. The system was born out of necessity before the 1984 Olympics and has since evolved into what's considered the eighth wonder of the transportation world, using sensors, algorithms, and human intervention to balance the competing demands of millions of drivers, pedestrians, and cyclists navigating LA's fixed street infrastructure.

The Birth of ATSAC: 1984 Olympics Crisis

With over a million visitors and thousands of athletes expected for the 1984 Olympics, LA faced a major transportation crisis. City officials worried that the already congested streets would prevent people from reaching events on time. Transportation official Ed Rowe assembled a team that created an experimental network connecting 118 traffic lights around the LA Coliseum, allowing engineers to monitor and adjust signal timing remotely for the first time. The system worked so well during the Games that Mayor Tom Bradley joked at the closing ceremony, "the Games are over, let the traffic begin."

  • LA was preparing to host the 1984 Olympics with more than a million visitors expected
  • Before 1984, all traffic lights in LA operated independently with timing mechanisms that could only be adjusted manually on-site
  • Ed Rowe's team connected 118 traffic lights around the LA Coliseum into a single networked system
  • The system reduced delay by 30-35% during the Olympics by allowing remote, real-time adjustments
" The Games are over, let the traffic begin. "
" We reduced delay at intersections by about 20%. We reduced stops by 35%. "

How ATSAC Works: The Brain Behind LA Traffic

ATSAC has grown from 118 signals to controlling nearly 5,000 traffic lights across Los Angeles. The system uses sensors embedded in pavement that count passing cars and feed real-time data to a downtown control room. Engineers monitor hundreds of cameras showing a 360-degree view of the city, and algorithms automatically adjust signal timing to smooth traffic flow. The control room has become legendary among traffic nerds and was even featured in the 2003 heist film "The Italian Job."

  • ATSAC controls almost all of LA's 5,000 traffic signals through sensors buried in pavement at most intersections
  • Engineers work in a downtown control room with hundreds of cameras providing a 360-degree view of the city
  • The system automatically extends or shortens green lights across interconnected intersections to help traffic flow more smoothly
  • The ATSAC control room has been featured in movies including The Italian Job and is considered legendary among traffic nerds
" Without this system, the streets of L.A. would be even more clogged. "

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