This isn't the case racedo. LHR has 180k pax a day, only 37% of which are transfer - and some of those will be travelling to a hotel for the transit. This ratio has been pretty stable for several years. If pax numbers double, this will put over 100k more pax arriving or departing each day. Living near to J13 M25 (immediately South of LHR), I can tell you that the motorway is at a standstill both ways at least once a day. Business pax, in particular, just do not want to use public transport, nor do most others, judging by the traffic on our frequent visits to T5.
The assumption here is that pax numbers double.................not in a very quick time frame.
Big question that nobody seems to be asking exactly where all these new passengers will come from.... I got no idea nor do I believe others have.
Thing is if currently there are 2.6 Million pax between LHR-NYC will there be 5 million post this.....................doubt it.