Traffic lights
When they first came out, traffic lights didn’t help regulate automobile traffic. They came a long way before cars became commonplace. Lights were used to help carriage drivers stop and go, preventing road congestion and road rage. We wonder what early road rage sounded like when people were still driving carriages.
Anyway, the modern traffic light has pretty much made traffic a lot easier to manage. Also, they’re programmed with preset times or by detecting which roads require freer movement to reduce traffic during certain times of the day. The 1920s saw the first three-color traffic light, with Detroit being the first to implement them at a city-wide scale.