1. Who invented modern traffic lights?

`to` Ko có đề cập trong bài bạn ạ.
2. When were Red-green installed?

`to` Red-green systems were installed in Cleveland in 1914.

3. What were installed in 1918?

`to`  Automatic signals were installed a year later.

4. How did they use to be operated?

`to` They used to be operated by hand from a tower in the middle of the street.

Modern traffic lights are an American invention. Red-green systems were installed in Cleveland in 1914.Three-color signals were installed in New York in 1918. They used to be operated by hand from a tower in the middle of the street. The first lights of this type appeared in London, on the junction between St.James Street and Piccadilly, in 1925. Automatic signals were installed a year later. In the past, traffic lights used to be very special. In New york, some lights used to have a statue on top. In Los Angeles, the lights did not just change silently, but would ring bells to wake the sleeping motorists of the 1930s. These are gone and have been replaced by modern systems that are seen everywhere now.