The first thing to understand about speed limits is the posted limit is the maximum, not the target.
I am lucky to drive a modern car that has the ability to identify the posted speed limit and it displays it on my windscreen. But if you aren’t diving a vehicle that has that ability, there is a simple way to identify the actual limit.
Now look at the picture, what is the speed limit? 30mph, 40mph or 50mph?
The correct answer is 30mph, and you can tell it’s a 30 mph limit because there are street lamps. If there is a system of streetlights, then it will always be a 30 limit unless signs say otherwise. So, the simple rule is: