Twin portal tunnel entrance double portal exit

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delt1c

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This may seem an unusual post, however got wondering many lines were built single track and then doubled with tunnels being 2 single bore. Got me wondering if their were ever any tunneles with 2 single bore entrance but becoming a double bore exit?
 
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Dr Hoo

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The Merseyrail Northern Lines have a mixture of single and double bores (built at different times) so a train from Brunswick to Sandhills enters a double (actually built for treble track) bore but emerges from one of a pair of singles.
 

IanXC

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Burdale Tunnel on the former Malton and Driffield Railway has a double track portal at one end and a single track portal at the other. During the course of construction the decision was taken that the line would be reduced from double to single track. It also allegedly includes an unplanned curve due to the two ends being off course during construction. It may not be surprising to learn that there were illegal drinking houses and riots during construction (!)
 

LNW-GW Joint

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I can't remember the exact configuration, but the stretch between Edge Hill and Lime St in Liverpool is a complex mix of 4-track cutting, plus 4-track, double and single track tunnels, all cut through magnificent Mersey red sandstone.
I guess it all depended when and how the original tunnelled section was expanded or opened up.
The Up Slow (northern side) navigates the most tunnel, while the Down Fast (southern side) is the most open.
 

Bald Rick

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The Canal Tunnels from the ECML to St Pancras are like this - double track portal at the ECML end, single bores when joining the Thameslink core at St Pancras.
 

edwin_m

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Connaught Tunnel on the North Woolwich Branch had double track ramps and bores each end, and a middle section with two single bores where it went under the docks. It's been heavily re-built for Crossrail but I'm not sure whether it was made into a single bore throughout.
 

swt_passenger

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Connaught Tunnel on the North Woolwich Branch had double track ramps and bores each end, and a middle section with two single bores where it went under the docks. It's been heavily re-built for Crossrail but I'm not sure whether it was made into a single bore throughout.
It is a single tunnel now, there’s an interesting video about how it was altered:
 

JN114

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The Heathrow Tunnels start out as a rectangular section cut and cover for the first few hundred yards (albeit with a “cosmetic” wall between the lines), which is the former trench the main tunnelling commenced from. It does then split into two single bores at Shepiston Lane escape shaft, with their own distinct alignments and gradients; the up line being shorter to Heathrow Central.

High Speed 1 starts out at the London end as a twin-bore tunnel/bridge over the ECML, before dividing into two single bores for the run to Stratford.
 

bramling

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The Canal Tunnels from the ECML to St Pancras are like this - double track portal at the ECML end, single bores when joining the Thameslink core at St Pancras.

That's an interesting one, as one could make a case to say that the "Canal Tunnels" end at the point where it transitions into the short section of box. ISTR that the latter section is recorded separately as a structure?
 

Bald Rick

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That's an interesting one, as one could make a case to say that the "Canal Tunnels" end at the point where it transitions into the short section of box. ISTR that the latter section is recorded separately as a structure?

It is, but is called the “Canal Tunnels Up / Down Tunnel Portal Section”. Therefore, still the portal!
 

bramling

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It is, but is called the “Canal Tunnels Up / Down Tunnel Portal Section”. Therefore, still the portal!

Now I thought it was "York Way Box Tunnel" (and I'm sure there's signage on the ground which uses that title). Is this a case of something which follows the railway tradition of having more than one name?!
 

Bald Rick

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Now I thought it was "York Way Box Tunnel" (and I'm sure there's signage on the ground which uses that title). Is this a case of something which follows the railway tradition of having more than one name?!

I was going by the Sectional Appendix; I suppose it might have had a name change.
 

AM9

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The Canal Tunnels from the ECML to St Pancras are like this - double track portal at the ECML end, single bores when joining the Thameslink core at St Pancras.
That's because the northbound tunnel dives under the TL (MML) tracks. I think the OP was implying where tunnels split for reasons other than them leading to different places.
 

Bald Rick

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That's because the northbound tunnel dives under the TL (MML) tracks. I think the OP was implying where tunnels split for reasons other than them leading to different places.

They both go from Canal Tunnel Junction (St Pancras) to Belle Isle Jn, arguably the same place!
 

Snow1964

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Not a tunnel, but a bridge. At Newbury Park when tube was extended it ended flanking existing tracks, so one side of an overbridge bridge had normal double track arch, the other side 4 tracks. The middle tracks were now closed route to Ilford
 

AM9

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Not a tunnel, but a bridge. At Newbury Park when tube was extended it ended flanking existing tracks, so one side of an overbridge bridge had normal double track arch, the other side 4 tracks. The middle tracks were now closed route to Ilford
I've refrained from citing instances where tube tunnels change from twin track tunnels to separate bores because there a quite a few if you count underground stations asnot in tunnels. Also many of them are because the separate bore ends serve island platforms or are fed outside the tracks of an existing twin track surface line,
e.g. Leyton (twin track) - Stratford (two single tracks), Central
Finchley Road (twin track) - Canning Town (two single tracks into close separate bores), Jubilee​
 

pnepaul

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Where does Linslade tunnel north Leighton Buzzard fit into. How did it reach its current configuration?
 

d9009alycidon

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Between Kelvinhaugh Junction and the SEC station the Eastbound track enters a single portal which breaks into the double track tunnel of the original Finnieston to Partick line and exits a double portal.
 

takno

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Doesn't the tunnel under Ryde on the Isle of Wight have that setup?
 

DelW

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Between Kelvinhaugh Junction and the SEC station the Eastbound track enters a single portal which breaks into the double track tunnel of the original Finnieston to Partick line and exits a double portal.
When I was working in that area about 15 years ago, it took me a long time to work out that layout - eventually I found a large scale map on line that showed how and where the tunnels met.
Doesn't the tunnel under Ryde on the Isle of Wight have that setup?
Two single track arches at both portals with a double track centre section. I suspect it was all cut and cover though, so the roof structure may vary along its length. One section apparently has a road above, carried on cross beams.
 

delt1c

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Between Kelvinhaugh Junction and the SEC station the Eastbound track enters a single portal which breaks into the double track tunnel of the original Finnieston to Partick line and exits a double portal.
I take it then this has a junction in the tunnel which is a rare thing on the national network
 

bramling

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I was going by the Sectional Appendix; I suppose it might have had a name change.

I had a look earlier. The twin tunnels both have signs stating “Regent’s Canal Up Tunnel” and “Regent’s Canal Down Tunnel”. The box tunnel has “York Way Box Tunnel”. In the structure register all three are numbered separately.

It’s a point of severe pedantry, however if we’re saying it’s twin tunnels emerging into a box at the St Pancras end, then I’d be more inclined to say the same applies emerging into a box at the Belle Isle end.

No right or wrong answer really! :)
 
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