Why has no-one considered re-designing Heathrow into a North-South layout?
You mean, apart from having to put 3 miles of the M25, a couple of miles of railway, and possibly a bit of the M4 in a tunnel, and paving over 3 reservoirs and a dozen gravel pits?
Or alternatively obliterating West Drayton, which some might argue would be no bad thing.
Yes, it's strange nobody else has come up with that idea.