Firstly, I'd like to say that I understand why the HS2-HS1 link has been sent for review. £700 million is a huge amount of money, and I can see how this cost could kill the project. Just looking at construction cost alone (stripping out maintenance/operations and the loss of capacity to NLL):
- 6% amortisation cost on £700M would be £42M/year
- 250 average days per year -> £42M / 250 = £168k/day
- 30 international trips per day -> £168k / 20 = £5,600 per train
- 200 average passengers per train -> £5,600 / 200 = £28 per passenger (£56 return)
(Please feel free to play with the above assumptions if you feel I've been too conservative/optimistic. I feel I've probably been too conservative there with the passenger/trip numbers.)
This £28 per person would just be for construction of the link aswell. It doesn't take into account
any other costs. Even so, it puts the link on a bad footing with respect to the low cost airlines already. So, I can see why the costs would have to be reduced.
Also, as much as I don't like it, I agree with some of the concerns raised by Camdenish folk about loss of capacity. I think they're possibly over-egging it, but they do have some valid comments. Effectively singling the line between Camden Road Station and Primrose Hill Station would have a devastating effect on the Overground in that area.
The cost
So what could be done to reduce the cost of the link? A look at one of the drawings gives a clue. From Old Oak Common, the HS2-HS1 link runs
in it's own tunnel until Primrose Hill Station, at which it joins the North London Line. I don't know the costs of each part of HS2-HS1, but I can easily imagine that this forms a huge part of the cost.
This seems crazy to me. Hopefully, when this gets reviewed, they will look at removing this tunnel for most of it's length and using the Old Oak Common to Euston tunnels as far as Primrose Hill. The link lines would then diverge from HS2 and meet in their own bore. I'm no expert on tunnelling, but I imagine that a solution could be found that was cheaper than six kilometres of single-bore tunnel. (And yes, I am aware that the stations on Crossrail are a big / the big part of the cost, but these point chambers would be nowhere near as large or as grand as these).
I am assuming that the section between Primrose Hill and HS1 is nowhere near as expensive as the tunnelled section, but as mentioned above, I'm no expert on tunnelling costs.
Perhaps someone can give me a rough idea of how much tunnelling is per mile, and therefore how much would be saved by eliminating roughly 6km of tunnel.
The North London Line - Capacity
Again, a quick look at the drawings suggests a large part of the Camdenites' problem. One track of the NLL would be taken and used by HS2, leaving the NLL single track (while carrying Overground and Freight services). If this could be avoided, then that would be preferable for all involved.
Fortunately, I think it can.
Primrose Hill Station is made up of a single island platform between the two lines. If the HS2-HS1 link is brought up between the two instead of to the south, then it can be linked to both without any conflicting moves. Instead of completely taking one track, the link would share both tracks. The loss to the NLL would be one or two paths per hour in each direction. This is what I have in mind.
I note on the above that the position of the tunnel portal would have to avoid the foundations for the bridge over the NLL at Primrose Hill. I can't tell from the aerial photos exactly where they are, but a bit of site investigation by the HS2 bods would sort that.
There would still be one conflicting move, as HS1-bound trains crossed over the Westbound NLL line, but one or two conflicts per hour is a relatively small price (in my opinion) compared to the loss of a whole track. The fact that international services would be a completely different market (and less in need of services during the peak hours) means that services could be optimised for NLL in peak, and HS2-HS1 (or freight) during off peak.
You may notice on the plan and long section above, that the third track would pass over a bridge to the east of Primrose Hill Station. This bridge serves the Juniper Crescent housing estate and the Morrison's supermarket. By my reckoning, and looking at the maps, there is approx. 400 metres between the tunnel portal and this bridge. The existing plans show a 3.5% maximum gradient for this section. Assuming 1.5% for the first 100 metres (allowing for change in gradient) and 3.5% for the next 300 metres gives (0.015 x 100) + (0.035 x 300) = 12 metres. This is more than adequate for our needs.
It might not be possible to raise the track to the above level and plumb it in, though. However, I don't see this as a problem. Looking at aerial photos of the area (thanks, Multimap), there seems to be enough room on the bridge for a third track. The bridge also looks new, suggesting that the drawings and design calculations of the bridge could be obtained relatively easily. It could then be shown that this bridge could support the extra track without rebuilding or extending.
One of the problems to deal with if HS2-HS1 shared tracks with NLL would be the gauging. The tracks would most likely require slewing to give the required clearance. However, the link track was supposed to be slewed in the original design anyway. This would not cause any additional cost to the project.
The next problem to deal with (moving east), would be the underbridge carrying the NLL over Camden Road and Royal College Street. I don't personally know whether these bridges can carry GC gauge trains. If they can, great. However, there is a risk that the east and west-bound decks will both need replacing. The west-bound one would have needed doing anyway, so this would not be an increased cost. The east-bound deck would be an addition, though, unless something could be done. However, this would be a deck replacement of the kind carried out by Network Rail umpteen times every year. NR have had far bigger challenges on deck replacements than this one.
The next issue is Camden Road Station. I can't see GC gauge playing well with platforms, as GC gauge is wider. I don't imagine the stepping distances would be appreciated by Network Rail and the Camdenados. This is the reason I think a single line was chosen, and which has led to the NLL-related protests.
Fortunately, I have a possible solution for this too.
- Rather than taking out the westbound platform completely, trim it back to allow enough space for 2 No. GC gauge tracks.
- Slew the westbound track to align with the platform, increasing the size of the six-foot.
- Put new rails for the GC tracks in the four-foot and the six-foot as shown below.
The new tracks would of course not be operationally separate, but that makes no difference. Track circuits would be the same (just connect the GC gauge lines electrically to the existing NLL tracks. Switching between the two would use something akin to normal points, which would be controlled by the signaller based on the train's head code.
I would note that this is not the only way to do this. I did think about retractable platform edges, but these caused more problems than they solved.
I would also note that Camden Road Station has two platforms currently out of use. One or both of these could be used while the above works were taking place, subject to the necessary plumbing in. In fact, in a more general case I could see this sort of thing happening in the long term anyway.
This would certainly help with mitigation of the paths lost to HS2-HS1, but for me would be more of a general NLL upgrade. I'm not sure whether or not it would be needed to replace capacity lost to the link.
Edited to add: do I get the prize for the best use of crayons?
