🚀 go-pugleaf

In article <1993Jan27.104508.24667@infodev.cam.ac.uk> rf@cl.cam.ac.uk (Robin Fairbairns) writes:
> The serious issue about the ultra-light weight cross-country trains is
> nothing to do with leaves.  Because they are so light, they have a
> tendency only intermittently to operate track circuits that detect the
> presence of trains on a portion of track.

This is a misunderstanding of the situation. The problem is not with all
ultra-light-weight trains - indeed, it does not happen at all with the
"bus bodies on rail wheels" abominations. The problem is actually rather
different.

When a rail is left unused for a day or so, it gains a thin layer of
oxide, which is an insulator. Normally this isn't a problem, because the
front wheels of the train hunt from side to side across the rail as the
train progresses, scraping the oxide off, and the remaining axles
operate the track circuits quite happily. The problem with the class 156
trains was that the design was so *good* that the wheels don't hunt on
straight track - instead, all the wheels follow exactly the same path on
the rail [1], and the oxide never gets removed. The solution is to add
"active shunts" which send a burst of electricity through the rails,
breaking down the oxide.

[1] Skeptics should note that the BR standard ride-quality test is to
stand a pound coin on the floor of the train.

> BR's reprehensible attitude to R&D again, I'm afraid.  If only they'ld
> spent more money, they'ld have anticipated the problem before they
> installed the current generation of track circuits, and made them
> behave more reliably in today's conditions.

The track-circuit problem only occurs when the line is used *only* by
the particular kind of train. This is quite a hard situation to test
for.

Anyway, BR aren't allowed to spend their own money on such things
(*all* expenditure on new stock has to be approved by the DoT, *even*
if they are spending extra income rather than PSO money).

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