Comment by pta2002
There's usually two - one suspended above the stop line, and one lower, on a pole on the side of the road, usually around eye level. This way both the driver in the front and drivers in the back get a clear view.
This is not a hypothetical "if", pretty much every country in Europe has traffic lights set up like this. Just take a look at Lisbon or Amsterdam in street view to see what I mean.
I’ve seen this in on-ramps but surely you can understand why duplicating traffic lights isn’t an ideal solution.