First of all this has doused my curiosity as per why race runners cluster themselves

Well, here is the answer. The outer track is longer than the inner one and thus, if a racer picks the outer track in a 400m race, he would need to run faster because he has a longer distance to cover and is most likely to get tired faster and lose the race (who would want to do that?).

Though not an automobile freak, but I leant something today 👆. I kept asking myself why can't these athletes just space out and run singly rather they cluster themselves. Lol 😀
Science is just awesome.
Thanks @rharphelle