2 Ideas for sorting out Herne Hill

[DJL]

Hi everyone, first post on here although I have been reading for a while.

I have some ideas and questions that I've built up over time but I'll start with this one.

Herne Hill is well recognised as being a rather large bottleneck on the CML and BML due to a large number of conflicting movements across 2 flat junctions.

As I understand it the issues with sorting this out largely revolve around it being technically challenging and also likely to cause an eyesore to local residents.

However this morning I came up with 2 ideas that may or may not have already been considered so here goes.


Option 1:
It occurs to me that a large number of trains that cross at Herne Hill have no desire to stop there.
Therefore it seems daft that the north and south junctions should be considered separately for any fly-over/under solutions.

I would propose that a new set of tunnels could be bored* underneath Herne Hill station with non-conflicting movements for non-stopping trains that stay on their own line.
Trains which transfer from one line to the other (i.e. a train going through Tulse Hill & Victoria or West Dulwich & Blackfriars) can continue to use the existing flat junction with reduced conflicts, as can stopping trains.

Advantages:

• no eye-sore
• fast trains would not even need to slow down
• Retains all existing cross-platform interchanges between existing services.
• No time-table changes required (although the minutes saved could be put to use).

Disadvantages:

• expensive
• does not remove all conflicting movements

Option 1b:
rework the flat junctions so that there are no conflicting movements at all for trains switching lines, although conflicts still remain for slow trains.

Disadvantages:

• No cross-platform interchange

.


Option 2:
Double-deck the entire station.
Step 1 - build a temporary junction where the line through North Dulwich crosses the CML.
This junction is likely to be slow, steep, tight and ugly.
Or build a different junction here, with an additional double-back loop in a field between the Peabody estate and Peabody Hill
Step 2 - demolish the existing trackbed between Herne Hill and Tulse Hill and change the gradient to rise up to a level above the current Herne Hill station.
Step 3 -Build a high-level station
Step 4 - to the north create fly-downs either side of the 2 existing lines.
Step 5 - Remove temporary tracks (or, if they are not hideous, keep them for emergencies)

Advantages:

• Removes all conflicts
• Likely to be cheaper than option 1

Disadvantages:

• Some cross-platform interchanges are lost
• A large eye-sore for the local residents.

I have identified gaps to the North and South of all 4 lines where additional alignments could be made with new gradients with minimal land required (although construction space could be tight with no line possessions)

What does anyone think?
Are existing plans already well progressed? Are they better/worse than my suggestions.

I will mock up some diagrams when I get a chance



* is Bored the correct word?
New tunnels could be bored, boared, born, constructed!

 

[MarkyT]

Hi everyone, first post on here although I have been reading for a while.

Hi and welcome.

Herne Hill is well recognised as being a rather large bottleneck on the CML and BML due to a large number of conflicting movements across 2 flat junctions. As I understand it the issues with sorting this out largely revolve around it being technically challenging and also likely to cause an eyesore to local residents

Quite a bottleneck I agree but probably less conflict now than when Eurostars passed through (up to 2 an hour in each direction).

I suggest a much cheaper tweak to relocate the Thameslink platforms to the centre, so each separate movement of a stopping train on that route only conflicts with one of the main line tracks at a time. That should make the junctions easier to operate, being similar to a highway 'centre turn lane' arrangement. see:

http://www.townend.me/files/hernehill.pdf

and

http://youtu.be/OpboBbCocnY

 

[Peter Mugridge]

It's on a viaduct; you'd have to go very deep and very far back to tunnel under it. Double decking it is probably easier, using the Victoria lines. Just have connections into the existing outside platforms for the stopping Victoria trains.

Would need a bit of viaduct widening though.

 

[Chris125]

'London Reconnections' have a good article on this issue - Unlocking Herne Hill and the Kent route to the City

So to conclude, it is clear that Herne Hill will always be a problematic node in the south London network. Grade-separation appears to be illusory, unless tunnelled all the way from Tulse Hill to Loughborough Jn as part of a grander scheme. But there are other options.

The task now is to weigh those options alongside other potential investments nearby, such as Brixton and Lewisham, and assess alternative portfolios of investments for CP5 and beyond – and, of course, to safeguard an alignment for further bay platforms at Blackfriars, so the additional trains have somewhere to go.

Chris

 

[southern442]

Probably the less favorable option but you could get some fasts to stop at Herne hill.

 

[Mintona]

Not really sure what the solution is with Herne Hill. I do think that if any work was to take place, it should include the provision of 12 car platforms, as at some point in the future I think all ex-NSE trains will be 12 coaches long. Don't spend £ms changing it now only to have to do it again in 15 years.

I think the best option is probably a 'double deck' station a la Tamworth, although you would then lose the ability to travel from West Dulwick to Blackfriars or Tulse Hill to Victoria.

 

[HSTEd]

Tulse Hill to Loughborough Junction is only 3000m.....

Tunnelling that far is not absolutely out of the question....

 

[Peter Mugridge]

Tulse Hill is also elevated isn't it? So the gradient required to get from the earliest possible start point to the required depth would be rather... interesting. Probably similar to Blackfriars to City; the length may be greater but the height difference required is also greater.

Whether tunneled or elevated, the Tulse Hill lines would need to be the ones left as they are and the Victoria lines the ones elevated or tunneled.

 

[DJL]

I'm not sure why everyone thinks the tunnels need to go so far.
The viaduct isn't all that high, or indeed long.
A short distance south of the junction the tracks are at ground level (on the cml certainly and from the aerial photo I'd guess the bml too, maybe an embankment for some distance)
Looking at the aerial photo of shortlands junction the newish dive under tracks for the Catford loop uses approx. 250m to get down sufficiently to be under the cml.
And the 319s handle that just fine.

So at herne Hill we would only need ~500m to get under both the station and the 1 road underneath it. And that is assuming the road itself can't be moved (look at Sidcup station )

The gaps I mentioned previously are between 500-750m either side of the offending road.

Actually, thinking about it, 1 pair of tunnels would have to be deeper to avoid another flat junction. This would have to be the bml tunnels as there is more space to the south for these .


Hmm, this post is starting to sound like I think I know better than everyone else.
This is not my intention! I'm happy to be told why I'm wrong.

 

[Peter Mugridge]

I'm not sure why everyone thinks the tunnels need to go so far.
The viaduct isn't all that high, or indeed long.

So at herne Hill we would only need ~500m to get under both the station and the 1 road underneath it. And that is assuming the road itself can't be moved (look at Sidcup station ).

In the case of Tulse Hill to Herne Hill, look at where the road is next to Tulse Hill station; it's quite elevated above the road ( the one that leads to the Tulse Hill Hotel ) there - then it's not all that far to Herne Hill and you don't just have to dive down below the road, you've got the viaduct foundations to think about as well. It's also on a rather noticable curve.

Even if just thinking about the road, you've got all the services under the road to worry about - sewers, electricity, water, gas and so on, so you'll still be going fairly deep and with not a lot of wiggle room to do it in

So between Herne Hill and Tulse Hill, you're going to end up with a steep gradient on a fairly sharp curve; not a good combination.

That's why any tunnels / flyovers need to be on the Victoria tracks.