As if they weren't quirky enough, for the longest time in the 20th century, French cars had yellow headlights. The reason why ...

From 1937 to 1993, the French government required all cars sold in the country to feature "selective yellow lights" for all forward-facing roadway illumination.

The light just turned yellow and you've got a tough decision to make. Braking doesn't seem right – you're going too fast for a smooth stop. But continuing to drive also doesn't seem right ...

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.