Maximum permitted line speed: Clapham - Croydon

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Big Mac

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Apologies if this has been covered before, but I can't find any previous references to this specific question.

The max line speed, on the fast lines, between Clapham Junction and East Croydon seems to be, from my observation of lineside speed limit signs, 70mph. Which is great. I was on a class 377 EMU at the time.

My mate had an 'app' on his mobile phone, which once we got going, indicated a near-constant 70mph speed shortly after Clapham, only slowing down just before Selhurst, presumably to navigate the complex junction located on the approach to East Croydon.

My question is: why is it that this run does not achieve a maximum speed more than that? Given there is a relatively sharp curve in the line between Balham and Streatham Common; could that be the reason?

Or could it simply be due to the relatively short distances between the stops, even though the train in question, given enough distance, is capable of 100mph, it would not be efficient to do so.

This isn't a moan; I'm just curious.

Thanks.
 
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notadriver

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It's to do with signal spacing. Also higher speeds require more expensive track maintenance.
 

Big Mac

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Thank you; yes, of course that is a limiting factor. Would the European Rail Traffic Management System (ERTMS) enable an upgrade of linespeed if that was installed?
 

notadriver

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I'm just guessing here but ultimately it comes down to the higher cost in maintaining track to that higher speed. Also increased energy usage.
 

Railsigns

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There's a trade-off between speed and capacity. Trains running at higher speed need longer distances to brake, so there has to be greater separation between following trains. ERTMS has the potential to help but the speed/capacity trade-off would still apply.
 

notadriver

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In some places in London where the limit is 70 mph on the fast lines I wouldn't like to go faster than that on account of the condition of the track.
 

The Planner

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There's a trade-off between speed and capacity. Trains running at higher speed need longer distances to brake, so there has to be greater separation between following trains. ERTMS has the potential to help but the speed/capacity trade-off would still apply.

Depends on what speed the signal spacing is for though surely, we could run Pendos around 90-120 seconds apart at linespeed on sections of the WCML fasts now and we plan on 3 minute headways, but conversely run a Class 4 at 75mph on the fasts and the headway would increase.
 

Peter Mugridge

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Given the volume of trains, nearly all of which call at both Clapham Junction and East Croydon, would not faster running mean they'd all just start catching up on each other and end up waiting for platforms?
 

notadriver

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The fast lines between Stratford and Shenfield used to be about 70 mph maximum. Now 90 is allowed :o
 

hwl

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Given the volume of trains, nearly all of which call at both Clapham Junction and East Croydon, would not faster running mean they'd all just start catching up on each other and end up waiting for platforms?

Indeed 18/19tph with long dwell times and a single platform at Clapham or in the other direction 40/60 (and some lower limits) at Windmill Bridge Jn and usually another train in front from London Bridge waiting to clear the platform at East Croydon.
No point in going any faster as you don't get there any quicker.

The signal spacing isn't set for high speeds either but rather the am peak crawl in the Clapham Jn.
 

neilb62

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There used to be an 'Inner London" maximum speed on all three Southern Divisions for a certain distance from the terminus, when I was at 'Vic C' it was 60mph maximum as far as Balham this I believe was due to the loading on the conductor rail because of the amount of trains. Also the section appendix modified the time a Driver waited at a signal before contacting the signalman in the same area, in this case from 2 minutes to 10.
 

A-driver

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BTW, the Balham curve mentioned by the OP has a speed limit of 60mph.


You sure? When I signed the BML the 70mph board was the London side of Balham. The fasts had a 45mph restriction for a while one summer due to the screeching noise on the curve but this has now been removed.
 
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