PainInDeArse,
Which, just as an example, is longer than the length and TORA at Southampton, for an aircraft to land short or go off the end and hit one of the circa eight trains per hour that pass by SEN would have to be one hell of a shot but for an aircraft to land short or go off the end at SOU, it wouldn't be one hell of a shot at all to hit just some of the hundreds of vehicles per minute that pass by the end of the runway on the M27 motorway!
And there is a track record of airliner(s) on motorway(s) in UK ... a BD B737-400 @ EMA springs to mind.
So why are you singling out SEN ... did they turn you down for a job or similar?