Wednesday, 16 March 2016

Liverpool HS2/HS3 Junction

I have given some thought to the junction that would link my preferred HS2/Liverpool link to
the planned trunk. The requirements I set were a straight through connection to Manchester without using the main north-south trunk, no increase in the set of points on the main trunk and keeping speed as high as possible.
In the end, I came up with 3 options the Option 1 fulfils all these criteria, with minimal changes to the existing HS2 phase 2 plan. Option 2 would require some changes to keep the number of points down, while Option 3 is the simplest and comprises most of the principles, but is the one with the least new land take but also the slowest speeds, due to the tight radii of the curves. In order to keep within HS2 already published acceleration and speed requirements the line around the junction would need to be quaded but this, I believe has been allowed for in the original plans. I have assumed that the route to Liverpool uses the Warrington and Altrincham Junction Railway at least through Warrington.
The maximum speed that seems acceptable on curves is given by the table below, the data is taken from Minimum railway curve radius with the diagrams I have had to approximate the curves.

Curve radius ≤ 33 m/s
= 73mph
≤ 56 m/s
= 125mph
≤ 69 m/s
= 154mph
≤ 83 m/s
= 185mph
≤ 97 m/s
= 216mph
≤ 111 m/s
= 248mph
Cant 160 mm, cant deficiency 100 mm, no tilting trains 630 m 1800 m 2800 m 4000 m 5400 m 7000 m
Cant 160 mm, cant deficiency 200 mm, with tilting trains 450 m 1300 m 2000 m no tilting trains planned for these speeds

North Junction

The existing proposal for phase 2 includes a junction north to east, I am not entirely sure why, given current plans have the GC route finishing before Wigan, any trains from Manchester north would have to be classic compatible and   already some routes north available via those, the same is true for Liverpool northward. So, for the purposes of this blog, I will consider the routes north to be optional though I will leave the existing planned line in red.

Option 1

DIagram of a junction bwteen a reinstated Warrington and Altincham line and HS2. The disused Altrincham line crosses from the west at thetop of the picture. A large chord curves around to the south connecting to the southern spur of the junction proposed in the HS2 phase 2 document, heading south. A reflex chord departs and joins the route into Manchester.
This arrangement fulfils all the criteria keeping to radii of over 5000m allowing running speeds of over 200mph. It would eliminate the north chord suggest for phase 2 and replace it with a longer chord further west. It would, however, entail going through 270 degrees to transit between Liverpool and HS2 north.
It is unlikely that such speeds would be permitted on the section of line from Warrington as it passes through some residential areas making the large radii redundant.

Option 2

A straight line departs from the Alricham line and heased south east crossing the route of HS2 and joing the manchester spur, a chord leaves half way along its lnegth and curves south joing the HS2 trunk heading south.
The simplest way to avoid some of the line speed restrictions would be to leave the Warrington Altrincham route earlier, to the west of Lymm close to the M6, to avoid steep turns it would mean leaving the route before the M6 so the existing under pass could not be used. It would involve taking a new cross country route of some 8km to link to the Manchester spur, with a chord to the south, which could use the same sets of points on the trunk as the Manchester spur.
To the north, the chord would have to be somewhat tighter and may involve adjustments to the north junction proposed for phase 2 in order to keep the points countdown. However,   geometrically it is the simplest junction and involves little change to the routings planned in phase 2.

Option 3

A very simple junction is provided with tight curves connecting the Warrington and Altrincham route to the HS2 route north and south.
This is by far the simplest option reusing the maximum amount of old right away and adding the minimum new track, it does this by sacrificing speed the curves from the Liverpool route to HS2 are of about 500-600m in radii limiting speed to 70 mph. There would no option but adding points to any northern routing.
However, if the section of line between the northern crossing was quad, all the way to and beyond the southern Manchester Spur, then the points in that direction could be kept the same and the quading would allow acceleration to full track speed. Access to Manchester is via the northern chord proposed for phase 2.
As a schematic it would look like


My simple conclusion is that Option 3 is the most likely. I doubt the extra speed of the other 2 could actually be realised. Option 2 may be the option that has to be picked to calm the noise concerns of the residents of Lymm.

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