Why yellow traffic lights were designed to be ambiguous

The yellow traffic light is a perfect example of imperfection — with intention. While driving you have to think fast. Do you speed up or stop, whether that means easily or slamming on the brakes? Every driver has their answer and what lies in the middle is a vast perceptual field. A great deal of thought has gone into the engineering of the ambiguous yellow light, as IDEAS producer Seán Foley found out. He had his own encounter with what he was sure was the shortest yellow light in the world. It resulted in a traffic fine, and gave voice to so many questions.