"The typical traffic light is roughly the size of a large table fan.
The hardware necessary to switch a signal from green to amber to red in a fail-safe way can probably fit into the space of an old desktop computer.
So why does Philadelphia need to install control boxes as big as refrigerators to operate its traffic lights?
Let's start with the Department of Homeland Security.
On orders from the federal government, Philadelphia is replacing all its electromechanical signal boxes with a digital system that will eventually host the guts for a citywide network of surveillance cameras. While the old signal boxes were small enough to be strapped to the poles of traffic lights, the new digital, camera-ready signals require a lot more space - freestanding cabinets 67 inches tall."