The third design reminds me a lot of a friend of mine's 2 lane with crossovers in the corners. I don't have a picture of his track with the crossovers in it - but they were placed mid corner,not at the entry or exit.
This picture from Scalextric isn't of an oval - but it matches how he has his placed:

I definitely wouldn't recommend it for racing with novices - but running non-mag Tran-am cars on his has made for great entertainment as it evened out both lanes and throws the twist of pass "timing" into things.
Whether that would translate on the larger three lane version, I can't say - but I have to say, it looks fun! :)