Like really, why tho?
In: 0
They have identifying marks on them so pilots know which runway and taxiways to use when ATC directs them. This is to avoid collisions and move aircraft around efficiently.
The numbers on a runway represent their heading on a compass divided by 10.
So runways are numbered from 1 to 36
This is to help identify them, make it clear to pilots where they are too land or takeoff to avoid accidents.
The big numbers on the tarmac are there to identify them to pilots visually.
It’s not all airliners with maxed out IFR instrumentation, you know. Aviation is also small planes only kitted out for visual flight rules. Straightforward marking helps prevent confusion and mistakes.
To tell them apart.
If a plane wants to land on a run way, there needs to be clear communication which one and in which direction so there are no collisions and accidents.
If the tower tells a pilot “you are clear to land on the runway”, the obvious question is “which one?”
You don’t want to play games about my left, your left, your other left when communicating which runway to use for landing or launching a plane.
You could use descriptions like the left-most runway pointing in a north-west direction , but that is not really a good way to communicate.
Instead they number them, according to direction they point. from 01 to 36 these numbers represent 10° to 360° degrees. They chop of the last zero and add a leading zero for numbers smaller than 10.
A runway that goes north-to south would get the number 36 or 18 depending on which direction you approach it from.
A Runway that goes north-west to south-east could be something like 04 or 22 depending on the direction.
If there are multiple parallel runways they get an L, R or C added to them for left, right and if there are three center.
The pilots have charts of the airport that tell them about the layout of the runways and the numbers are painted on them as a sort of last resort if all else fails.
Printing numbers on the runway makes it clear in good weather conditions which runway is called what. Mixups happens sometimes in this respect, and can get nasty if not noticed.
The runway number is also usually the approximate heading of that runway direction divided by 10.