Double track inside a portal becoming single track outside the portal

The question was: does anyone know of a tunnel on a real railroad (what ever that actually means) were a tunnel is double tracked but, the tunnel approach is single track. Where the single track approach diverges into t a double track shortly before entering the tunnel?

I can find many examples of double tracked tunnel BUT, not with the approach being single tracked.

Many examples of double track converging into single track into the tunnel but, that's not what I'm looking for.

| -----+------------------- out in the open ---single--track diverge inside the tunnel -----+------------------- |

The Swiss Gotthard tunnel has a somewhat similar and also unusual arrangement.

The main line is twin track and it continues through the tunnel as a twin track single bore. Goshenen station is immediately ouside the tunnel entrance and on a very restricted site at the head of a valley. To provide a headshunt for the station tracks there is a separate twin track bore about 100 feet to the east of the main bore.

The headshunt bore only penetrates a short distance into the mountain and then a double track crossover joins the headshunt tracks to the main line tunnel which BTW is one of the World's major ones at 15 kilometres long.

Not in a tunnel as such but the Bakerloo Line of the London Underground runs on the surface mostly North of Central London. Just North of Queens Park Station, where some trains terminate, there is a multitrack train storage shed which straddles the double track main line and through which the service trains to/from stations north run while carrying passengers. This is a standard gauge line on the surface with a very frequent service though a "Metro" type line rather than a regular main line and the train shed is a conventional surface building rather than a tunnel.

Sorry to reply to my own post but I have just found a relevant photo.

the tunnel entrances viewed from the station platforms, with the main line bore being on the right.

Unfortunately the picture doesn't speak for itself. I can't see where the double track comes out of the tunnel and becomes single track.

Paul

I didn't say it became single track. In fact I clearly stated the main line was double track. The headshunt tracks on the left are also double track.

What the situation somewhat resembles is that hypothesised where the double track in the tunnel extends for only a short distance or is out of service.

Paul, Whatever it is worth.....I find two schools of thought in this hobby....those who copy, and those who make things up...sometimes inspired by the prototype. The hobby is about limitless imagination and that is what makes it great. Everything on my layout is this way including two tracks coming out of a tunnel and merging into a single track.............why?? One quarter of a mile up is a single track bridge and a single track tunnel just ahead of it. Sure, planning ahead maybe would have had the two tracks merge into one on the other side, but at the time plans had been made for a double track tunnel and the double track to continue on, but drilling became more difficult and way over budget for the next tunnel up the line , so a compromise was made. Any number of rationales can be made for this situation. That is the challenge and enjoyment...at least for me. Have fun, HZ

I'm a civil engineer, and I am not aware of any situations like this. As has been pointed out previously, tunnels are expensive to build and they would be just about the last place on the line to be double tracked if/when traffic warranted it.

On the same note, I can't think of a situation where a railroad would begin a double track *after* it entered a tunnel as a single track (but I have to admit that I am less certain of this possibility than the latter).

That being said, however... railroads make their decisions on keeping construction and operating costs low -- and if they faced the same constraints that model railroaders and their layouts faced, I am SURE that they would prefer to keep their switches in the open before entering the tunnel portal! And in that regard, having the turnout before the tunnel is the scaled-down "prototypically" correct thing to do!

- Mark

Apologies, I mis-read your post the first time.

Not specifically 3 tracks but there are places, usually in urban areas wheere several tracks go underground. I do believe that the 4 tracks of the Horseshoe also enter tunnels on either end of that particular scenic piece of track.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Starting from the apex of the curve and going east, no tunnel until you get to Spruce Creek some 20 or so miles away. There are two tunnels there. In the Good Old Days, the 4 track main dropped to 3 tracks, 2 into one tunnel, 1 into the other. Don't know what it looks like today. I think it is 1 track in each tunnel, but I'm not sure.

Back to the apex, go west. Three tunnels at Gallitzin (top of the mountain). Two parallel tunnels, 2 tracks through each. The third tunnel sat off to one side, was single track. There was another track came up the hill from Hollidaysburg which was the main user of the third tunnel. Again, that was a while ago. Today, one of the two main tunnels is unused, two tracks through the other, one through the "odd" tunnel, although now the separate track from Holllidaysburg is no more.

No 3 or 4 track tunnels near Horseshoe Curve. Never, so far as I know.

Bob Netzlof

Guess that shows what happens when you assume that there are tunnels there. I went there once but didn't find that the area was that great compared to some other places. It's also interesting that there is two bores rather than one for the tracks. I guess that the trackage got built up to the 4 tracks gradually and making a second bore was cheaper than opening up the one bore as they were able to do the second bore without affecting the first bore.

-- Why isn't there an Ozone Hole at the NORTH Pole?

I had been thinking present day scenario but I re-read my books on the Gotthard Tunnel and paid more attention to the early history of the line.

While the main tunnel and many of the structures on the approach tracks were built to suit double tracks, the line was opened in May 1882 with single track throughout.

The tunnel itself being so long that it tested the technology of the time. The approach tracks on both sides being very difficult and involving long, steep continuous gradients and spiral tunnels, economies had to be made and laying only single track at first was one of them.

The line was doubled in sections, the first near Bellinzona, near the southern end, and the second through the main bore itself.

So the situation would exist where the track up to the station at the north end of the tunnel was single, there was a few hundred yards of multiple track through Goshenen Station where there was an engine shed and then double track through the tunnel.

At the southern end of the tunnel there is a smaller, less important station, just outside the portal at Airolo. Again, immediately past the end of the platforms, is the top of the southern approach ramp. This would give, for several years, double track in the tunnel and single track on the approaches outside. The line was, of course, worked by steam until electrification in the 1920s.

It took many years to double the entire length of the line, with the last section, over a causeway at Melide near the Italian border, not being completed until the 1960s.

One possible reason for doubling the tracks through the tunnel before the approach tracks is that the area is subject to very heavy snowfalls with three or four metres deep drifts not being unusual. A tunnel is a ready made snowshed. A similar excuse could be made for the model track arrangement on the OP's layout

Now, that line arrangement has reached the limit of its capacity and a new base tunnel, much longer and eliminating both the approach ramps, is under construction.

Great, thanks. Any books with pictures that you are aware of? I've been googling but, all the links I find in google quickly go into German (I think?). Any pic's that you know of on the web?

Paul

The two books I have with information on the construction of the Gotthard line and tunnel are (1)"The History of the Gotthard Railway" by M. Hardy-Randall, published by John Cocking, Swiss Book Servive, Salisbury, England. 1997. ISBN 0

953184 0 2.

This is a large, comprehensive book, size 8" x 13 3/4" and runs to 509 pages covering most aspects of the line including drawings of the structures, locomotives and rolling stock. It includes several maps and track plans including Goshenen station in 1882 showing the two tracks in the tunnel and single track on the approach line. There are also some photographs of the line under construction and early operation.

My other book is in German, "Die Bahn durch den Gotthard" (The way through the Gotthard) by 5 authours and published by Orell Fuessli, the largest Swiss publisher, in 1981. ISBN 3 280 01258 9

Page size is similar to the English language book and there are 250, with many pictures in colour. It also covers much the same ground as the other book.

Assuming both books are still in print or available on the second-hand market, I would suggest the first book would be your best bet.

I don't think there are all that many photographs out there from the

1880s as this was also very early in photographic terms. I did do a Google "Images" search on "Gotthard tunnel" which produced 395 pictures, including lots of the new base tunnel construction.

I did not look at them all but did come across one of an early train leaving the south portal. This was also in the first book but did not really show much in the way of trackwork as there was rather a lot of smoke and steam.

There may be others but I'll leave it to others to view all of the images. :-)

I also have three separate editions of "Die Gotthardbahn" by Marti & Trueb. These editions each have mainly contemporary pictures of virtually the whole line,from the 1970s and 80s, different for each edition. There is only a brief historical section to each book so there are not nearly so useful as the two books listed above.

Hope this helps.

gradually

That, and think about the geometry of a tunnel.

Given an arched roof, as the width of the tunnel is increased the volume of material to be removed above the spring line of the arch increases in proportion to the square of the width, assuming the same shape arch.

So, two double track tunnels would require less excavation than one four track tunnel.

Another motive might have been to avoid putting all the eggs in one basket. If something bad happens and the roof of one tunnel caves in, there's a good chance that the other one won't. I think I heard of just that happening at Spruce Creek some years ago.

Bob Netzlof

...

First attempt to locate the book didn't look like it was in print or available. I'll keep poking around though.

I'll sepnd the time.

Quite a bit, thanks. Paul

Try looking at this site.

was the only used book that found and it is in France.

-- Why isn't there an Ozone Hole at the NORTH Pole?