Talking of this area - even over the last two (Southern strike) days, our Thameslink runs were crawls between Loughborough Junction and Norwood Junction. I couldn't see any TSRs, so is there some sort of blanket 15mph limit on this entire stretch? We, not surprisingly, had greens all the way, but still crawled.
It will take time writing this so bare with me, I'll explain speeds and why it takes forever.
The run from elephant to loughborough junction is 60 mph
From the junction before loughborough junction to the start of the platform 20 mph.
Loughborough junction to herne hill 60 mph
Across the junction and up to peabody viaduct 20 mph,
From the viaduct to the junction before tulse Hill 45 mph
Across the junction and into tulse Hill 15 mph
Tulse hill all the way up the Norwood spur, through West Norwood and about 1/3 of the way to gypsy hill 20 mph (this is the low speed long slog)
A short stretch of 35, the 50 mph from before gypsy hill until the exit of crystal palace tunnel.
15mph across crystal palace junction.
25 through the platform.
50 mph to Bromley junction then 20 to Norwood junction.
Another reason for the slow speed is you have to wait for the rear of the train to clear the previous speed restriction, I'm not good at maths but it takes a 12 car train 3 times as long to go through a 15 mph restriction than a 4 car. This all adds up.
One example is coming out of crystal palace tunnel southbound the speeds go 15/25/50,
in a 4 car as soon as you get to the 4 car monitors you accelerate to 25, clear the platform then it's upto 50.
In a 12 car you have to wait until you are all the way through the 25 and we'll into the 50 before you clear the 15, you then accelerate upto 25, by the time you clear the 25 you can get upto 35 before braking for the 20 at Bromley junction.
So I feel a 12 takes longer in the slow section compared to 4 or 8 cars.