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West Anglia Main line Diverts

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MatthewRead

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I've noticed that the West Anglia Main Line is closed on several weekends through Tottenham Hale and trains are being diverted via Seven Sisters what does this mean for the London Overground service to Cheshunt via Southbury?
 
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AlanFry1

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Nothing really more than stations between Theobald's Grove and Seven Sisters being a bit more busy
 

Ianno87

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What I mean is will the West Anglia trains being diverted via Southbury have an effect on the Liverpool Street to Cheshunt services?

Nothing - both Cheshunt and Enfield Town have their normal 2tph off peak frequency.

It's GA that take the hit - Stansted Express is reduced to 2tph, and Hertford East operates 2tph to/from Broxbourne only. Then 2tph Cambridge makes up the numbers.
 

Ianno87

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...and obviously the 2tph Bishop's Stortford-Stratford do not operate at all. So all in all the usual 10tph via Tottenham Hale is reduced to 4tph to fit via Seven Sisters.
 

sjoh

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6tph no? 2x Stansted, 2x Cambridge, 2x Broxbourne (why couldn't these continue to Hertford anyway?)
 

sjoh

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No, 4tph. The Hertford trains operate from Hertford to Broxbourne, not London to Broxbourne (as you said, no reason they can't go to Hertford!)
Ah! Gotcha. Cheers!

Presumably this means that there are off peak paths via Seven Sisters for fast services during normal operating environment - they're just not used?
 

Ianno87

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Capacity is governed by the approaches to Liverpool St (2 tracks in from Bethnal Green, the flat junction there, and 1-7 throat capacity at Liverpool St), so while there is space via Seven Sisters it can't necessarily be used for any extra trains.

It is essentially what permits GA to run 14tph on West Anglia in the peak - 2tph between Liverpool St and Hertford operate via Seven Sisters (using the spare capacity of this route) as the Tottenham Hale route is full with the other 12tph. But then Liverpool St is absolutely full with 22tph (so further space at Seven Sisters can't be used)

It does give however some amount of diversionary capacity should there be an incident/blockage via Tottenham Hale.
 

sjoh

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Ah okay - so the other 2tph paths through SVS can't actually be used unless 2tph are cut from the Hale route into/out of LST? Makes sense.
 

Ianno87

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Apologies - just had another look

GA do manage to get all 4tph Stansted Express via Seven Sisters, albeit with extended journey times, in addition to 2tph Cambridge (so 6tph GA in total). Repeating half hourly Down pattern is:

Enfield
Stansted
Cambridge
Cheshunt
Stansted
Enfield etc...
(i.e 2 trains run behind the Enfield service that gets out of the way at Bury St Jn, with 1 train following the Cheshunt which is in the way for longer)

To get it to work, Hertford East only runs to/from Broxbourne, and Bishop's Stortford-Stratford doesn't run at all.
 

AlanFry1

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I don't understand why they can't retime trains north of cheshunt going southbound, and south of cheshunt going northbound. so they're not right behind one of our slow LO stopping services?
 

Ianno87

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Two issues:
-Timings at Cambridge are pretty fixed. Both in terms if fitting around GTR and also keeping the 'normal' standard pattern for the likes of Audley End. XC to/from Stansted are also pretty immovable. Once you've fixed all that the Stansted single line pretty much dictates the usual pattern for Stansted Express having to apply. So it easier to just bodge everything onto the Southbury Loop
-The number of the stations on the Southbury Loop means that it's pretty much inevitable that fast trains are going to catch slow trains up. No amount of clever timetabling can sort that out.
 

Be3G

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Presumably this means that there are off peak paths via Seven Sisters for fast services during normal operating environment - they're just not used?

Ah okay - so the other 2tph paths through SVS can't actually be used unless 2tph are cut from the Hale route into/out of LST? Makes sense.

A Rail Utilisation Study quite some time ago (probably about a decade) proposed building a turn-back siding at Seven Sisters to unlock the extra capacity of which you speak without interfering with Liverpool Street services but sadly nothing became of it. Always a pity I thought, I'm sure the Southbury loop would do well with 4tph considering how busy the nearby road (bus) corridors are.
 
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