Crosrail has morphed into Heathrow connectivity which to be fair is bizarre. It was always designed to support Londoners in the West getting to the East
Crossrail was always marketed as a link to LHR. BAA partly funded it and one of its main selling points was the fact you would be able to get from Canary Wharf to LHR in 30 minutes. There is nothing bizarre about it unless you are ill informed.
but there will also be journeys in and around LHR caused by businesses, families and individuals who have located in the area because of its proximity to LHR.
Do you know how many people live in the Thames valley and work in West London? Also the amount of traffic that goes between the M1/M40 and M3/M4? Much of this has nothing to do with the airport.
The fundamental point remains that additional journeys on this busy section of the road/motorway network, caused by an expanded LHR, results in a requirement for expensive construction of additional road capacity.
The fundamental point remains that this busy section needs expansive construction at some point between now and 2050 whether we get a third runway or not. This is based on current levels of traffic no matter where you think they are coming from. As a result it would be far more cost effective to do this in combination with the airport expansion. To then try to say we should not build the new runway because these works are so expensive misses the point. Combining large infrastructure projects of this sort provide a huge cost saving and minimise disruption.
To build an upgraded interchange around LHR anyway, have Crossrail and HS2 running into it and the Western rail link onto the GWR, then choose to favour Gatwick for expansion is just crazy.