Interesting fact that maybe I'm the last person to discover, but...
I'd long wondered why underground trains came in 2 obviously different sizes, ie. the central line AKA the sardines express vs the district line, the carriages thereof being properly capacious.
Was talking to a TFL'er who said it annoyed him that all tube trains were collectively referred to by the public as 'underground trains' when there were actually sub-surface trains (the big ones) and proper underground trains (like the central and northern). I really hadn't known.
Edit: he could also tell the line a (proper) underground train was on by the metallic shriek it made. I asked him what caused that and he thought it was the wheel flanges rubbing on the sides of the rails during tighter turns.
> I'd long wondered why underground trains came in 2 obviously different sizes, ie. the central line AKA the sardines express vs the district line, the carriages thereof being properly capacious.
Because the original lines were opened in the mid (sub-surface) to late (deep) 19th century. The sub-surface lines were built cut-and-cover and thus easy to make roomy with the technology of the times, digging from up and covering was well within easy means, however the deep lines were built using pre-TBM tunnelling shields, limiting their diameter due to effort and sheer technology. The deepest station in the underground was opened in 1907, remains one of the deepest stations in the world, and pretty much all the deeper ones opened after WWII.
Later deep lines (Victoria and Jubilee) I'm guessing were kept at the same diameter for convenience (of sharing structure, infrastructure and rolling stock), and possibly existing sections being "moved" from one line to an other.
> Was talking to a TFL'er who said it annoyed him that all tube trains were collectively referred to by the public as 'underground trains' when there were actually sub-surface trains (the big ones) and proper underground trains (like the central and northern). I really hadn't known.
Technically they're all underground trains, as in trains which are part of the London Underground. The sardine express ones are "deep-level" or "deep-tube" (they used to be the actual tube lines but the term has expanded to basically be the same thing as the Underground).
I'd long wondered why underground trains came in 2 obviously different sizes, ie. the central line AKA the sardines express vs the district line, the carriages thereof being properly capacious.
Was talking to a TFL'er who said it annoyed him that all tube trains were collectively referred to by the public as 'underground trains' when there were actually sub-surface trains (the big ones) and proper underground trains (like the central and northern). I really hadn't known.
Edit: he could also tell the line a (proper) underground train was on by the metallic shriek it made. I asked him what caused that and he thought it was the wheel flanges rubbing on the sides of the rails during tighter turns.