the speed limit is enforced when it is in sight of a person
In the UK the speed limit comes into force as soon as you pass the speed limit sign. As such the distance is zero as you should have slowed down to the posted speed limit before passing the sign.
The posted speed limit is the max speed.
the posted speed limit
826 limit
You can be ticketed for traveling at an unsafe speed regardless of the speed limit.
Whatever the posted speed limit is.
When it is flashing the speed posted is the limit
The maximum speed limit.
In most states, the speed limit in a school zone when not posted is typically 20 mph.
If the posted speed is not safe at that time
When another speed limit sign is reached that changes the limit from the previously posted one.
When there is no speed limit sign posted on a road, it means that drivers should follow the default speed limit set by the law for that type of road.