Signals, Sensors, and Smart Streets: USC ITE Visits LADOT ATSAC

Have you ever wondered who decides when a traffic light turns red or green? On October 3, 2025, members of USC’s Institute of Transportation Engineers (ITE) visited the Advanced Transportation System and Coordination Center (ATSAC) at the Los Angeles Department of Transportation (LADOT) for a behind-the-scenes look at how LA manages its complex web of traffic signals.

Located on the 11th floor of the Caltrans District 7 building in downtown Los Angeles, ATSAC serves as the nerve center for the city’s traffic operations. Our host, Jeannie Shen, P.E., Transportation Engineer at LADOT, introduced us to the team responsible for keeping the city moving smoothly. Our faculty advisor, Professor Eric Shen, also began his transportation career at LADOT, making this visit even more special.

ATSAC was originally established in 1984 to help manage traffic during the Olympic Games near the Coliseum. Back then, it operated just a handful of cameras and detectors. Four decades later, it now oversees nearly 5,000 traffic signals, 600 cameras, and thousands of detection devices linked by both wired and wireless communications. Whether it’s a weekday rush hour or a weekend filled with events, ATSAC staff are constantly monitoring real-time traffic data, coordinating across jurisdictions, and implementing strategies to reduce congestion. From the San Fernando Valley to San Pedro, wall-to-wall screens display live feeds of intersections across the city.

We learned that ATSAC cameras monitor traffic in real time only! They do not record footage, perform tracking, or share video control with law enforcement. Their purpose is purely operational: to verify traffic conditions and coordinate field crews through two-way communication.

Many students admitted they had never paid attention to traffic control devices before, such as in-pavement inductive loop detectors, aerial cameras, or signal cabinets found on nearly every street corner near USC. During our tour, we even watched the live camera feed from the intersection of Jefferson Boulevard and Hoover Street near USC Village. Next time you walk by, see if you can spot the camera yourself!

Jeannie explained different signal operation modes, such as pre-timed, semi-actuated, fully actuated (also called “free operation”), and the more advanced adaptive mode, where groups of signals adjust their timing based on live traffic conditions. We also learned about the cost and maintenance trade-offs between loop detectors embedded in pavement and newer video detection systems. Every technology decision, Jeannie emphasized, must balance functionality, cost, and long-term reliability.

Among the fun facts we picked up: jaywalking is more common on the East Coast, where most signals are pre-timed and less responsive to pedestrian activity. We also discovered LA’s only reversible traffic lane on 4th Street, and how emergency vehicles and Metro buses can communicate with signals to receive traffic priority.

Jeannie reminded us that even the most advanced systems eventually become outdated, and that future engineers must learn to make the best use of existing tools before designing new ones. As it turned out, just hours after our visit, streets around City Hall were closed due to a security incident. For the ATSAC team, there’s truly no such thing as a dull day in Los Angeles traffic management.

Thank you to Jeannie Shen and Professor Eric Shen (yes, they are related) for giving us an inside look at the technology and teamwork that keep Los Angeles moving.