//One or two more carriages on commuter trains would make a world of difference. //
this has already happened on the routes into Waterloo, where trains are now 10 coaches instead of 8. there has been a huge investment in trains, and in lengthening all the platforms to accommodate them. this was completed 2 years ago and already the extra capacity this realised has been used up, and more. lengthening trains to 12 cars not practical without massive changes (removing and replacing bridges, alterations o tunnels, demolition of lineside houses, etc) to make room for longer platforms. pretty much everything that can be done to squeeze a quart into a pint pot (bit like smart motorway work on the roads) has been enacted, and the extra capacity already exhausted.