In 1916, the first traffic tower was put up in new York, at the intersection of fifth avenue and 42nd street. A traffic officer controlled three 500-Watt lamps. They measured 40 centimeters in diameter, and they were red, amber, and green. However, at the time, red meant traffic in all directions had to stop, amber stopped only east-west traffic, and green stopped only north-south traffic. This was very confusing, so in 1924 the city adopted the system used in railroads: red for stop, green for go, and yellow for slow. This system became standard all over the world.