The yellow light would not come into play until the 1920s. William Potts, who was a police officer in Detroit, is credited for designing the first three and four-way colored traffic lights.

The yellow light didn’t enter the scene until the 1920s. William Potts, who was a police officer in Detroit, is credited with designing the first three- and four-way colored traffic lights.

The first traffic signals were not red, yellow and green. Here's why they are now.

Today, 101 years after the installation of the first modern, three-lens traffic light, yellow is the new green. Red is the new yellow. Green is the new red. It’s all very mystifying.

Henry Liu, a civil engineering professor who is leading a study through the University of Michigan, said the rollout of a new traffic signal system could be a lot closer than people realize.

Researchers say drivers might spend a lot less time waiting for the lights to change if cities added a fourth white traffic light colour to the familiar red, yellow, and green.

The yellow light didn’t enter the scene until the 1920s. William Potts, who was a police officer in Detroit, is credited with designing the first three- and four-way colored traffic lights.

Smarter vehicles could mean some of the most dramatic changes for the traditional traffic signal since the yellow light was added more than a century ago.

The yellow light didn’t enter the scene until the 1920s. William Potts, who was a police officer in Detroit, is credited with designing the first three- and four-way colored traffic lights.

Smarter vehicles could mean some of the most dramatic changes for the traditional traffic signal since the yellow light was added more than a century ago.