TC - Traffic Concentration, a large marshalling yard like Toton where trains could be dispatched local or further afield and remarshalled as required.
What era was this? The 1981 BR booklet of location terminology has TC defined as "Terminal Complex" -
Sidings tied exclusively to the shunting requirements essential to service sidings at a major terminal or group of terminals
*may also perform a marshalling function for Speedlink trains or sections of trains
The only use of "concentration" (apart from coal concentration depots) I've seen is for "Mansfield Concentration Sidings." In the caption to this rather nice 1976 photo of coal traffic in the sidings, this location is described as "the yard where N Notts coal was gathered for forwarding, principally to ER destinations like Whitemoor and New England yards."
https://www.flickr.com/photos/auchlander/5274519591 (Photo: Auchlander)
I mentioned in post #50 that "Network Yard" and "Terminal Complex" didn't really catch on as names, but looking through freight working timetables from the 1980s, it's noticeable that a lot of yards were either designated as T.C. (Terminal Complex) or S.S. (Section Sidings), the latter defined in the 1981 booklet on location terminology as:
Sidings, the function of which is to form or break down local network wagonload trains to or from one or more Network Yards in order to service by trips, Terminal Complexes, Terminals, Sidings or Departmental Depots in the area
I noted these names from a selection of WTTs dated between 1989 and 1992:
Acton T.C.
Alexandra Dock Jn T.C.
Bescot Down N.Y.
Cambridge T.C.
Cardiff Tidal T.C.
Carlisle N.Y.
Craiginches S.S.
Darlington Up S.S.
Didcot T.C.
Eastleigh N.Y.
East Usk Jn N.Y.
Falkland S.S.
Fratton S.S.
Garston (Speke) T.C.
Gloucester N.Y.
Hither Green Down Recp.
Hoo Jn S.S.
Immingham S.S.
Ipswich S.S.
Laurencekrk F.D.
Llandudno Jn T.C.
Kings Lynn T.C.
Millerhill S.S.
Mossend N.Y.
Northampton T.C. (Down)
Northampton T.C. (Up)
Norwich T.C.
Norwood Down S.S.
Parkeston S.S.
Perth T.C.
Peterborough West S.S.
Plymouth Friary S.S.
Radyr Junction S.S.
Redhill RECP.
Ripple Lane East S.S.
Ripple Lane West S.S.
Salisbury S.S.
Southall T.C.
St Blazey S.S.
Temple Mills S.S.
Thames Haven T.C.
Three Bridges P.A.D.
Tonbridge S.S.
Southampton Up T.C.
Southampton Down T.C.
Stranraer Town F.D.
Swansea Burrows S.S.
Thornton S.S
Tyne N.Y.
Westbury Up T.C.
Westbury Down T.C.
West Drayton T.C.
Whitemoor N.Y.
Woking Down Recp.
Woking Up Yard Recp.
But there are other locations retaining more familiar names in the WTT, e.g.
Ellesmere Port West Sdgs
Ellesmere Port East sdgs
Willesden Brent Sdgs
Toton Old Bank
Toton North Yard
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This changeover to the use of "Terminal Complex" and "Section Sidings" didn't happen straight away after the publication of that 1981 booklet. It appears that these official terms were gradually rolled out during the early 1980s, but I suspect few railwaymen working in these locations regularly used these terms.
I think a term like "Network Yard" for Speedlink was applied in a similar way to the use of a contemporary term like "Local Distribution Centre" for infrastructure traffic. For example, in the 1981 booklet on location terminology, "Doncaster NY" includes West Yard, Up Decoy and Down Decoy. In a similar way, the modern "Doncaster LDC" would include both Up Decoy and Wood Yard (along with Belmont Yard). The individual yards retain their original names in everyday use (and within TOPS / TRUST) even if their official function is as part of Doncaster LDC.
The term "Section Sidings" adds a bit of confusion since the S.S. abbreviation previously meant "Sorting Sidings."
In a May 1982 WTT for the Western region (Section PE), SS is included in the list of abbreviations as "Sorting Sidings," along with YD for Yard, HS for Holding Sidings, RECP for reception sidings and RS for recess siding.
The same WTT for May 1984 expands this list considerably to include NY for Network Yard and TC for Terminal Complex, along with various familiar abbreviations for different types of terminal. SS is included but is now defined as Section Sidings rather than Sorting Sidings. The London Midland region also included a list of abbreviations in their WTTs around the same time, largely matching the terms used in the western region. Other regions didn't seem to bother defining these abbreviations in their WTTs but still followed the same conventions; for example the Eastern region had "Tinsley N.Y" and the southern had "Eastleigh N.Y." and "Hoo Junction S.S."
The RmWeb thread linked below is quite interesting, and one post suggests that the terms "marshalling" and "sorting" fell out of favour for "political reasons" - I assume to avoid the negative association of these terms with the kind of yards that had been closed over recent years, and to introduce new terms that were suggestive of a modern efficient wagonload network.
https://www.rmweb.co.uk/topic/172370-railway-yard-meanings-and-hierarchy/
In any case, the term "Sorting Sidings" was less applicable once hump shunting came to an end, although it survived in the names of some of the signal boxes around Basford Hall, as seen here at Crewe Sorting Sidings North in 1990:
https://www.flickr.com/photos/ingythewingy/45154816824/ (Photo: Ingy The Wingy)
The abbreviation "NY" also causes a bit of confusion at Carlisle, since the marshalling yard built at Kingmoor as part of the modernisation plan was already known as the "New Yard." However, Carlisle N.Y. as seen in a WTT from the 1980s onwards means "Network Yard." A 1976 WTT simply refers to it as "Carlisle Yard."
