Inspired by my three year old as I could not give an answer.
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According to [https://kutv.com/news/get-gephardt/good-question-who-decided-red-means-stop-and-green-means-go](https://kutv.com/news/get-gephardt/good-question-who-decided-red-means-stop-and-green-means-go)
>The answer, according to multiple sources, predates cars on roads. It was established by rail roads. About 200 years ago, as tracks began spanning the globe and getting more crowded, British train companies decided they needed a way to communicate to train conductors to avoid accidents. They came up with traffic signals.
>They deemed red would mean stop because red was already widely used to signal, “Danger.” They decided a clear, unfiltered white light would mean go.
>That’s the way it was for about 100 years, until 1914. One night a red filter fell off a light making it visibly white. It signaled a train conductor to go and led to a pretty big wreck.
>To make sure the accident would not repeat itself, the train industry decided to do away with clear lights and made green the signal to go.
>As horse carriages and eventually cars began filling roadways, the highway folks stole the color scheme.
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