KNOX COUNTY, Tenn. — When Knox County Schools released its back to school plan in July, it based everything on a color-coded system of red, yellow, or green. Basically, green days would be ...

There are a few reasons why the colors red, yellow, and green were chosen for traffic lights. Red is an obvious choice. The color red means danger or to be alert for something occurring.

Eventually, the upgrades could do away entirely with the red, yellow and green lights of today, ceding control to driverless cars. Henry Liu, a civil engineering professor who is leading a study ...