Both the Lhr options are not thinking laterally. At the moment the M25 at this point is regularly grid locked so putting more traffic on it is going to make it chaotic. Also has anyone considered the construction phase for several years the road will become a nightmare
Have little impact on M25 for additional PAX as plan would be to continue to get transit passengers. In addition public transport would get an uplift.
In relation to construction then as most would be done one site I would see this minimised with local roads bearing brunt for materials but this can be shipped in at night or construct an offshoot from a rail line to deliver materials in from a staging area well outside London.