A traffic light (1 "light" composed of 3 lights) or A SET of traffic lights (3 lights considered individually)?

Question

Which is idiomatic in British and American English, when talking about a single post that contains 3 lights, red, yellow and green? A traffic light or A SET of traffic lights?

Dictionaries seem equivocal about this.

• The Longman Dictionary of Contemporary English lists only the plural noun traffic lights. This implies that each of the red, yellow and green lights are considered separately.
• The Oxford Advanced Learner's Dictionary lists a singular form traffic light, with a note that says "(also traffic lights [plural])", and a definition that says "a set of lights that controls the traffic on a road." Based on this definition, the singular form seems to be able to refer to all three lights together.
• The Cambridge Advanced Learner's Dictionary would beg to differ. Like the OALD, it also lists the singular form traffic light, but the definition says "one of a set of red, yellow, and green lights that control the movement of vehicles", meaning that a "light" really means a single light, not a set of three lights.

There have also been multiple spirited online discussions. Two Wordreference threads (1 and 2) seem to arrive at the conclusion that traffic light is idiomatic in the US, while traffic lights is in the Commonwealth. More users from italki seem to agree with this intuition, too.

If it is indeed the case that traffic light is American English and traffic lights is Commonwealth English, I guess the only thing left is confirmation from an authoritative source, preferably some sort of book or guideline from a transport(ation) authority.

Answer 1

The California Driver’s Handbook calls the set of lights a traffic signal. A traffic signal has lights of different colors:

A yellow traffic signal light means CAUTION.

In conversation, a passenger would probably warn the driver by saying “There’s a light up ahead.” “Turn left at the light” would be idiomatic in the United States, as would “Turn left at the third traffic light.”

Answer 2

Based on the information you provided from the dictionaries and online discussions, it seems that there is some regional variation in the idiomatic usage of "traffic light" and "traffic lights." While it might not be possible to find a definitive answer on this issue, we can infer from the information available that:

1. "Traffic light" tends to be more idiomatic in American English, referring to a single post containing the red, yellow, and green lights.
2. "Traffic lights" seems to be more common in British and Commonwealth English, where it can refer to a single post containing the three lights or multiple sets of lights at an intersection.

It's important to note that context plays a significant role in understanding the intended meaning. In most cases, speakers of either American or British English should be able to understand what is meant, regardless of whether the term is used in singular or plural form.

However, it is worth noting that language is always evolving, and what might be considered idiomatic today might change over time. To get a more authoritative answer, you could consult transport authorities or style guides from both regions.