Traffic Light Meanings

The other day I was driving and came upon a flashing yellow light which I had never actually seen before.  I had a memory of it being in my new driver's manual but since I hadn't had to use that knowledge it had slipped from my memory.  I slowed down and "proceeded with caution" which when I looked it up later was apparently what I was supposed to do.  While looking it up I started reading the Wikipedia page on traffic light signalling and found out a lot of things I didn't know.

The first most general thing I learned is that traffic lights across the world can be very different!  I haven't done any driving outside of North America so it was interesting to read about the quirks of different traffic light schemes.  There are various ways to indicate turning, different circumstances where flashing lights are used and a few ways to indicate a changing light.  If it interests you I'd recommend just reading through the Wikipedia page, but I'll list some of the things I found interesting.

Flashing green lights mean different things in different places which can be dangerous in some situations.  In parts of Canada a flashing green light, also called an advanced green, means that you have permission to make a left turn and that the opposing traffic has a red light.  In BC however it means that the traffic light is pedestrian controlled and other than that is the same as a normal green light!  For people driving in BC from other parts of Canada this could definitely cause some confusion.  In some parts of China flashing green means "reduce speed now".

Apparently in Tianjin, China they have a horizontal bar traffic light system.  The bar is green, yellow or red and shrinks to indicate the time remaining for that colour.  A disadvantage of this system is that color blind people will have trouble differentiating between the colours, although apparently people who are colour blind are not allowed to have a license in China!

One other thing that I wasn't aware of was what's called the "yellow trap".  It occurs when a driver is waiting at a green light for a left turn and the light facing them turns yellow but the opposing light remains green.  The driver may expect that the oncoming traffic will be stopping shortly and begin to make a left turn possibly resulting in an accident.  I actually didn't know that some lights in opposite directions weren't timed to switch to yellow and then red at the same time.  From the article, "Some of this stems from difficulties programming older traffic signal control software to prevent the yellow trap, but much stems from traffic engineers or technicians not understanding the yellow trap hazard, or believing it is not a serious problem."