like most debug stuff in games it mainly meant for testing game physics and game behavior.
it appears the numbers around that pole are for perhaps testing vehicles turn radius. (mainly to make sure the computer is keeping track of car position properly and isn't drifting off course. (driving around in a tight circle)
it could also be to test/adjust brake distances at various speeds. (IE brake at the pole and see where you stop.) if it stops too soon, it could make the game too easy, if it takes forever to brake it can make the game unplayable
The track can (could have been) be modified by programmers to do really anything they want by just plopping a couple models here or there. this just happens to be the last thing they tested.