London Banter - View Single Post

Mike Bristow · February 18th 16, 09:27 AM posted to uk.transport.london

In article ,
d wrote:
On Wed, 17 Feb 2016 16:33:55 +0000
Mike Bristow wrote:
I don't have a good grasp of the cost/benefit ratio of your proposed
scheme. I don't think you do, either. But feel free to prove me
wrong by estimating the cost of installing - and maintaing for a
decade, say - a set of points, and the benefit of doing so - again,
expressed in cost terms.

Feel free to tell me why the actual cost matters, rather than as a percentage
of the total cost of the ELLX.

Becuase spending £1,000,000 for a £2,000,000 benefit is worth doing.
But changing the plan so you spend £1,000,001 for a £1,999,999
benefit means your change isn't worth having. Or changing the plan
so you spend £1,000,001 for a £2,000,000.01 benefit makes your
change daft.

Don't forget to include the cost of increased delays when the points
fail. Obviously, you'll know the MTBF for points - I'd be interested
in knowing what that is, as it happens, so can you share your
estimate for that, too?

I imagine the MTBF would be the same as other sets on that line. When was
the last time any of them failed and the line had to be closed because of it?

So you don't know? How can you estimate the disbenefit of additional
points if you don't know the MTBF (and the cost of the failure)?

I'm quite happy to say there are things I don't know. TfL did spend
a lot of time removing reversing facilities on the tube - I think

Oh didn't they just. Every time there's a problem on the piccadilly line half
the damn line has to close. Genius.

Given that you don't know really basic things required to assess
the change, I'm not sure you're qualified to judge. (I'm not sure
I'm qualified to make that assement, though... I don't know much
about railway operations).

--
Mike Bristow