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Post by Deleted on Dec 6, 2009 18:37:31 GMT
(I searched for topics but could find any info - but redirect me if already covered).  I know that mileage on the Underground is measured from the former Ongar. I read recently that this was switched to kilometers in 1972 from miles and chains. Some questions: 1) Before the Central Line got extended past Liverpool street in the '40s, where were the distances measured from? Was it different for each line? 2) Would they ever redo the zero-point now that Ongar is long-gone - or would that be way to much work and expense? [Plus it is still on the historic railway scene.] |
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Post by Deleted on Dec 6, 2009 20:08:34 GMT
(I searched for topics but could find any info - but redirect me if already covered). I know that mileage on the Underground is measured from the former Ongar. I read recently that this was switched to kilometers in 1972 from miles and chains. Strictly, (1)"measured from Ongar" is one of those simplifications that can lead to difficulties if not understood: "measured based on a system with zero datum at Ongar" is perhaps a better way of putting it and (2) "mileages" have never been based on Ongar, only kilometrages - the Ongar datum was adopted c1972 as part of switch to metric distances. There is some description of the system on CULG (Clive's Underground Lines guide) here I did a post about on the Yahoo Tubegroup here - quote: Re: Measuring
The 'Quail' or 'Metric' system (presumably it has an LT/LU official
name, but I don't know it) works on the basis of marking/measuring
distances along (each) line - and these are marked (on the ground)
with a plate every 200m. These just indicate the (relative) distance,
related to some datum, so plate 54.0 is mid way between (and 200m
from both) 53.8 & 54.2, and is 54 km from the (its) datum point.
When the system was designed, a spart of a full re-survey at the
beginning of the seventies, two considerations were (1) there should
be no negative points and (2) that it should be co-ordinated across
the system, with as few 'jumps' as possible (i.e. wherever possible,
at a junction the sequence would follow through for both branches).
These two considerations led to the zero point having to be at one of
the furthest extremeties of the systems, and was fixed at Ongar (the
other option would have been a bit beyond Amersham, at the LT/BR
boundary). From there the main Central Line just has a simple
sequence through to both West Ruislip and Ealing Broadway. Now we
start on the complexity! For the Hainault loop, the sequnce is
followed through at Leytonstone - so effectively it is measured from
a datum point there (at about 26.4) with decending kilometrages round
to Woodford Junction (at about 12.0 in that sequence - which ends (or
starts) there). So when we see 17.0 at Hainault that doesn't mean
it's 17 km from Ongar, but rather it's at that point a seies which
ends with 26.4 (or so) at Leytonstone (where it matches the distance
directly from Epping). The next 'complexity' comes at Mile End, which
was defined as the place where the Central & District sequences would
be matched. So Mile End is at 33.07 (according to Quail) on both
lines, and this forms the datum for the District Line sequence, which
descends east bound to Upminster (to about 11.1 at the far end of the
depot), and ascends westbound (to Ealing/Richmond/Wimbledon). And the
Piccadilly Line is sequence is then set from that so that from Barons
Court to Hanger Lane Junction (i.e. the shared bit) the District and
Piccadilly sequences match... (But when you do get to Ealing Broadway
the District and Central are 'out of step'). And so it continues
round the system. While it is easy to refer to all these as plates as
marking distances from Ongar this is a (possibly over)
simplification. For many purposes it may be better to regard them as
a consistently related set of datum points...
Anyway, I hope that clarifies things - appologies if anyone thinks
they've just had an egg sucking lesson.
Most of the rest of the British railway system is still measured in miles and chains (with many different datums, which can be difficult to determine) I believe BR considered a similar 'kilometrication' exercise to LT, but decided it was too complex and expensive to be worth it. One of the things to be remembered is that one of the purposes of such a system is to record where things are, so changing it introduces a lot of issues. Quail is the name of a publisher who produced track maps of British railways (including), showing mile and kilometre posts - it (or its successor) is now callled Trackmaps. Yes - prior to 1972 each section had its own set of mileages. I can't see it happening: it would a major effort for little or no benefit. |
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mrfs42
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Big Hair Day
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Post by mrfs42 on Dec 6, 2009 20:43:37 GMT
Yes - prior to 1972 each section had its own set of mileages. The mileages would be published in the WTT or in the 30s the UERL group published tables (in miles and tenths of a mile) in their Appendices as ready reckoners - the Picc. and Bakerloo were published as reversible tables, the Hampstead and City were Edgware to Kennington via CHX and Highgate to Morden via Bank, the Central was a non-reversible table; in the MDR Appendix there were several tables: Manky House to Ealing Bdy, the Richmond Line was a hybrid, shewing 8 columns (ManHo, Edgware Rd, High St, Earls Ct, Hammersmith, Turnham Grn, Gunnersbury, Kew Gardens) against 4 rows (Turnham Grn, Gby, Kew Gdns and Richmond) - a similar thing applied for the Wimbledon, Uxbridge and Hounslow lines - with South Acton added into the mix where appropriate; Mansion House to Barking and the Circle was shewn in three columns distance from preceding station, distance from Mansion House (via Blackfriars) [ascending down the page] and (via Cannon Street) [descending down the page]. Mansion House was the zero point for the District, Liverpool St for the Central, Highgate for Morden via Bank, Edgware for Kennington via Charing Cross, Finsbury Park for the Picc and Elephant for the Bakerloo. There were footnotes for Kennington Loop, Wood Lane (Local) - Shepherds Bush, Hammersmith to : Hm Sidings, Barons Court Sidings and Lillie Bridge, Holborn - Aldwych, Finsbury Park dead end, KX (Picc) - Euston and Edgware to Highgate via Mornington Crescent. All distances were centre of platform to centre of platform. |
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