The inherent inefficiency of the three-light traffic signal is clearly demonstrated in this proposal for a two-light LED system, which produces the same three colors in one enclosure by combining red and green. Unfortunately, it still can't melt snow.
New-fangled LED traffic lights last longer, pierce the darkness more effectively and consume 90% less energy than incandescent bulbs. That's also their drawback. They're not hot enough to melt snow that sticks to their lenses, causing dozens of accidents.