The Reason For This Speed Restriction at Redhill?

[Deepgreen]

I took this photo on Monday 18 April looking north from Redhill and have only just noticed a slightly odd thing - the speed restriction is 75mph after the the line becomes plain two track (and is through the station behind the camera), but then rises to 80mph shortly after, on the same stretch of track (but before the facing crossover) - my question is; why not have it at 80mph at the nearer sign? Utter trivia, but just curious, as there seems to be nothing different about the two sections of line. Better detailed route infrastructure knowledge than mine may have the answer!

 

[Nicholas Lewis]

I took this photo on Monday 18 April looking north from Redhill and have only just noticed a slightly odd thing - the speed restriction is 75mph after the the line becomes plain two track (and is through the station behind the camera), but then rises to 80mph shortly after, on the same stretch of track (but before the facing crossover) - my question is; why not have it at 80mph at the nearer sign? Utter trivia, but just curious, as there seems to be nothing different about the two sections of line. Better detailed route infrastructure knowledge than mine may have the answer!

That does seem a nonsense - what speed are the through roads?

 

[headshot119]

The nearer and smaller 75 sign is a repeater, and is probably there to indicate to trains leaving what I presume to be a siding on the left that the main line speed is 75. The 80 is a larger start of restriction style sign, and indicates the line speed has risen to 80. What the reason is for the 80 from that point I don't know.

Pure speculation, the 75 repeater, could predate the raising of the line speed beyond to 80, which has lead to the rather odd situation you see in the photo.

 

[westcoaster]

It's a repeater shows the current line speed after an adjoining junction.
The line from the left is a 40mph section of track heading north out of platform 0 at Redhill.

 

[rower40]

It's a repeater shows the current line speed after an adjoining junction.
The line from the left is a 40mph section of track heading north out of platform 0 at Redhill.

Agreed. If the 75 sign wasn't there, a train travelling away from the camera, having used the line on the left, would have to stay at 40mph until it reached had wholly passed the 80 sign.

 

[Railsigns]

If the 75 sign wasn't there, a train travelling away from the camera, having used the line on the left, would have to stay at 40mph until it reached had wholly passed the 80 sign.

It wouldn't have to stay at 40 mph. Speed reminder signs (in fact, all speed signs) are only there to reinforce drivers' route knowledge.

 

[Deepgreen]

Agree with all of the above (I should have mentioned that I realise the small signs are repeater/reminder signs), but my question was why can't the speed limit be at 80 at the nearer sign as there appears to be nothing to prevent that - i.e. the formation, infrastructure, sighting, etc. all appears to be exactly the same as the section where the 80 limit begins a bit further on. I wondered if there is a 'hidden' infrastructure reason for keeping the limit at 75 as is. BTW the line joining from the left is the elongated loop serving platform 0 (and which used to be the up siding).

 

[JN114]

Agree with all of the above (I should have mentioned that I realise the small signs are repeater/reminder signs), but my question was why can't the speed limit be at 80 at the nearer sign as there appears to be nothing to prevent that - i.e. the formation, infrastructure, sighting, etc. all appears to be exactly the same as the section where the 80 limit begins a bit further on. I wondered if there is a 'hidden' infrastructure reason for keeping the limit at 75 as is. BTW the line joining from the left is the elongated loop serving platform 0 (and which used to be the up siding).

By starting the 80 restriction earlier; that changes the “attainable speed” at the next signal for trains starting from a stand in the platforms; and the proportion of the signal section that is at the higher linespeed.

If you fiddle with the speeds or attainable speeds approaching signals; you then have to fiddle with TPWS placement and potentially even signal spacing (although the latter is unlikely for the change you suggest here). With a relatively complex layout behind the photographer moving signals and TPWS grids may not have been possible within the confines of the station to allow the 80 to start earlier.

It should be noted the rather extreme telephoto effect in the picture betrays how far apart those speed signs are - almost 1/4 of a mile.

 

[Deepgreen]

By starting the 80 restriction earlier; that changes the “attainable speed” at the next signal for trains starting from a stand in the platforms; and the proportion of the signal section that is at the higher linespeed.

If you fiddle with the speeds or attainable speeds approaching signals; you then have to fiddle with TPWS placement and potentially even signal spacing (although the latter is unlikely for the change you suggest here). With a relatively complex layout behind the photographer moving signals and TPWS grids may not have been possible within the confines of the station to allow the 80 to start earlier.

It should be noted the rather extreme telephoto effect in the picture betrays how far apart those speed signs are - almost 1/4 of a mile.

All good points - thanks. Yes, a zoom lens does foreshorten.

 

[GB]

deleted

Ignore previous comment. The 80 sign is not where I thought it was!

 

[Snow1964]

There appears to be another crossover to the right after the 80 sign, which doesn’t appear to have a speed restriction sign (unless it is just not visible in the photo)