Rail Sign, New to me

[Bullfield WEst]

There is a sign by the track visible on the "Bedford Rail Cam" I have tried to guess the meanin of it but have given up, anyone help me out, please?
The sign states "TB" over "210m"

 

[Deepgreen]

The only acronym meaning that leaps to mind is 'Turn Back' - is there a siding there to which this could refer, with 210 metres being its length?

 

[swt_passenger]

It’s a “turnback“ marker. Where to stop the train when reversing on a running line. I’m not sure if it’s at a position meaning 210m maximum train length, or it’s an advance warning of something 210m distant.

you can see a 285m version on this page on the railsigns website:

Stopping Markers

 

[Snow1964]

Is the 210m the max length,
if so seems a strange choice, as 8car EMUs are about 161m and 12car EMUs about 242m and would be too short for a 5+5 class 810

Anyone know why a turn back that is wrong length for trains operating on the line would be specified ?

 

[Bullfield WEst]

Is the 210m the max length,
if so seems a strange choice, as 8car EMUs are about 161m and 12car EMUs about 242m and would be too short for a 5+5 class 810

Anyone know why a turn back that is wrong length for trains operating on the line would be specified ?

Thanks for the answers. I did see for the first time a 12-car Thameslink train stop and reverse yesterday evening.

 

[zwk500]

Is the 210m the max length,
if so seems a strange choice, as 8car EMUs are about 161m and 12car EMUs about 242m and would be too short for a 5+5 class 810

Anyone know why a turn back that is wrong length for trains operating on the line would be specified ?

210m may simply be the available operational length, and it is not practical to move signals or whatever for the 240m of a FLU. However it would be silly to post a lower limit than that actually achievable. Especially if you had a situation where an 8-car unit was being top/tailed by Locos for a stock movements (161m + 2x20m locos = 201m, 5m standback from signals either end).

 

[AM9]

Is the 210m the max length,
if so seems a strange choice, as 8car EMUs are about 161m and 12car EMUs about 242m and would be too short for a 5+5 class 810

Anyone know why a turn back that is wrong length for trains operating on the line would be specified ?

A 9-car class 222 is just under 208m. Could it not be for turning them?

 

[Supercoss]

8 car 700 = 162 metres long ( RLU)
12 car 700 = 243 metres long ( FLU )
to aid in T urn B acks , signage installed to indicate when train is rear clear of position light signal, rather than using more traditional black triangle on white circle .
210 and 285 m allows for adequate signal sighting for driver to view ground signal from seated position in cab