The person who invented the original traffic signal patented it in 1923 (http://www.google.com/patents?id=EHJoAAAAEBAJ&printsec=frontcover&dq=1475024&hl=en&sa=X

The person who invented the original traffic signal patented it in 1923 (http://www.google.com/patents?id=EHJoAAAAEBAJ&printsec=frontcover&dq=1475024&hl=en&sa=X&ei=fmXqTsSwI4G3twexk9ztCQ&ved=0CDMQ6AEwAA http://www.google.com/patents?id=EHJoAAAAEBAJ&printsec=f...). The idea was unique, novel, and non-obvious at the time. It's easy to see an invention now that is ubiquitous and say that it's obvious.