Copy-pasting my comment from elsewhere in the discussion:
"""
If someone on the west coast wants to ship to the east (or vice versa) they can pit UP against BNSF, and then NS against CSX. There are several pairs up because of the two negotiating points:
* UP-NS
* UP-CSX
* BNSF-NS
* BNSP-CSX
If the merger goes through you're now at:
* merged-UPNS
* BNSF-CSX
Do you think UPNS will give a cheaper price for a 'half-trip' and you go to their competitor the other half?
"""
In this case it's not even about non-overlap, it's a straight reduction of competition. You don't think BNSF/CN/CP aren't looking at CSX right now?
Freight rail is not an eyeball market, the customers are the ones paying.