Having been the B.R (W.R.) London Division Accident Clerk for 5 years during my railway career, I think that the reason why sides of this footbridge are so high is to prevent attempted suicides. This is a very lonely spot and anyone considering such an act would soon realise its potential!! On the other hand, anyone determined to commit such an act would reach the line by some easier means.
Apologies for contacting you concerning such a morbid subject.
Wishing you a long life, Martin Budd.
Many thanks for your comments Martin and best wishes to you as well!.