The green or white signs with numbers that are placed along interstate highways are mile markers.
They give travelers a way to determine where they are along a route.
The mile marker shows the number of miles from where the interstate route entered the state you are in.
For north–south highways, the numbering begins at the state line in the south; for east–west highways, it begins with the state line in the west.
If the interstate originates within a state, the counting starts where the highway begins.