Red Light, Green Light: The Science Behind Traffic Signal Systems

Jan 25, 2016

Here's a riddle for you: What's green and yellow, but most often red?

Give up? It's a traffic light -- you know, those things you hit on your way into the office each morning. But how do they work? And why don't they ever seem to be synced up? 

This hour, we explore the science behind traffic light programming. We hear from engineers and experts in Connecticut and Utah. We also find out how new "smart" signals are improving traffic flow in Pittsburgh, Pennsylvania. 

And later, if you've ever gotten turned around while driving through downtown New Haven, you’re not alone. We learn how converting from a one- to two-way street system could make the city safer and easier to navigate.


  • Jack Carey - Associate at Fuss & O’Neill, an engineering consulting firm in Manchester, Connecticut
  • Lisa Miller - Traveler Information Manager at Utah Department of Transportation
  • Stephen Smith - Research Professor in Robotics at Carnegie Mellon University
  • Doug Hausladen - Director of Transportation in New Haven; Acting Executive Director of the New Haven Parking Authority

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John Dankosky and Chion Wolf contributed to this show, which originally aired on December 18, 2015.