This Metro thing is a red herring.There is little difference between the current rolling stock and a Metro and no one has ever used the current rail halt even when every train stopped there.
Picture the scene. Myself, my wife , complete with holiday hair do and two children leave our house. Walk 3/4 mile to the rail halt and board the Metro, dragging 4 suitcases and assorted hand luggage with us. Did I mention it was driving rain and hail? Pay £20 each way to travel to the airport which takes 35minutes and at the other end have a 1/4 mile walk to the terminal . The rain of course is now coming from a different direction , soaking what few parts are not already soaked.
Second scenario. We load the car, drive to the airport in 30 minutes. Unload near the terminal entrance thus saving the holiday hair do and pay £32.00 for two weeks parking , £8 less than the Metro fare.
The only thing missing are the flights to take me on holiday .
Metro ? I don't think so.