wizo
a 2nd runway at STN for existing movements could in some circumstances be considered environmentally friendly - fewer holds for takeoff/landing at peak, fewer diversions due to a runway being closed due to an aborted takeoff perhaps. However, to accomplish this govt policy would have to be to fund such infrastructure on that basis, not on cost recovery which would demand an increase in overall movements, leading to more congestion, a third runway (see LHR).