The trains hate this part of the journey.
The very act of leaving their tunnels to be exposed to the grim light of Perivale causes them to slow and strain between the blocky houses and piles of refuse.
They sing to themselves, an oily-sweet music of groaning couplings and whining wheels. It doesn't help. The journey trails and drags to the passengers, too, and the very soul seems somehow sordid by Northolt.
It's all to do with sex.
Even the Underground symbol itself is a sign of penetration; the warm, dark tunnel of red, slid through effortlessly by the serpentine blue bar of subtle strength. The uncocooned part of the journey, then, is the return to the prosaic after the Great Ecstatic Mystery, apres petit mort.
Post coitum omne animal est triste
The undead genitalia-by-proxy of the bygone engineers are intended to journey through the long dark noisy spaces below ground. They wither and shrivel in the sunlight, even the tarmac-filter ersatz of Ruislip. The proper authorities know this, of couse, and try to make their wheeled Freudian charges feel at home by adding the occasional arch or tunnel over the exposed track. This is, to the trains, and unwelcome act of unsatisfying masturbation, and adds to the general feeling of indignity that seems to permeate the journey.
At the height of the moralistic campaigns of the '80s, a young vicar in the employ of the Civil Service was sent to convince the lustful locomotives that their behaviour was unacceptable. In order that they would not prove to be a bad influence on the young. He was not seen again.
It just goes to show, you don't fuck with the trains.