460 is about 106 metres
and the 400 is about 144 metres
The tracks normally have discs, or lines on the inside or outside of the tracks fences or railings

I'd bore you with the maths to calculate but the 400 takes in bit of the turn so you need to use centripetal formula for the calcs and the other matter that complicates it, is the T formula for acceleration as they hit the turn around the 95% top speed

Now if you look at the watchdog how they calculate straight time/distance you will find an edge.