Can't really meaningfully make those kinds of calculations without a whole-system look at aggregate flows in the UK. And the dataset for that is not really practically available in one place.
(Location of all significant quarries, location of all significant downstream aggregate depots and material flows between each pair)
Every depot would not have its own dedicated conveyer system to all possible source quarries.
And thats before we get into the second-order impacts on how the existance of such a system would alter the economic dynamics of the aggregate industry beyond the gross terms (it would likely speed the consolidation, given that something like
half of all crushed rock permitted reserves in England and Wales are at 115 sites with permissions expiring in 2042).
EDIT:
At best I have
this, but this obviously gives no clear indication on how each site is related.
EDIT #2:
This is also rather off topic - so perhaps we should park this, create a new thread or a mod should split this one?