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By the way, regarding branching off (not just) high-speed lines, that is a constant hobby-horse of mine...

The simplest solution is branching like a tree:

No superstructures, just four switches (like the one below: not only the end but the centerpiece is movable, too), one train passes three of them.

But such a simple bifurcation (AFAIK the one at Courtalain on the LGV Atlantique was such for some transitional time) is a bottleneck. To allow two trains to pass, you need at least one bridge:

If train control foresees switching tracks there must be such switches on one arm. So one superstructure, six switches, one train passes 3(4). Most high-speed line connections and bifurcations are like this.   Most of them in Italy, as the Italian high-speed philosophy involves connections to conventional lines every 30-50 km, often built out in a pharaonic way:

On a very busy line, it would be ideal if track-changing at the branching would be level-separated, too. What to do? One could double the tree:

But 4 superstructures, 14 switches, every train passing 5 -- expensive, and this number of routes is overkill. The following still  does all 12 cases, but spares 2-2 bridges and switches, and switch passages for one train can be 3-4.



*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Sun Mar 25th, 2007 at 06:12:24 PM EST
[ Parent ]
My focus above is on branch/main line junctions, rather than main/main line junctions, and branch/main junctions should be designed so that through services run through without switching. And this being the US, on a switch onto the end of the branch line (if the branch is to be accessed two-way, this is on the other side of the flyover, not in the main corridor)

So:

  • pull the main line alignment apart to allow a central track;
  • have the switching loop branch off one of the two main lines;
  • have the other main line switch onto that; and
  • fly the switching loop out of the main line corridor.

There is at least one switch on the branch line end, more if its a dual-track line or a t-intersection for access in both directions. If its a two-way Express alignment, then it would have the identical alignment on that end, so four switches total to interconnect the HSR corridor with a two way Express alignment. Add two more switches if a standing loop is required on the interconnection line.


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 11:12:42 AM EST
[ Parent ]
My focus above is on branch/main line junctions, rather than main/main line junctions

The switches used being high-speed switches, what I posted applies equally for 'branch/main' and 'main/main'. What may have been confusing is that I just didn't draw up the other end where the branch reaches the conventional line, which can be built as a mirror image of the high-speed junction, or simpler, depending on line speed and frequency (and number of tracks). The lots of Italian interconnections mentioned (& photo-documented -- the one shown is the Interconnessione Cassino, at the foot of famed WWII flashpoint Monte Cassino) are such.

For single-track access (which I'd generally advise against -- keept it double-track at least on the acceleration length, or until it connects to the conventional line), yours is fine, except if you fly over only from one side and connect on the other side, the through tracks can remain straight.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Mon Mar 26th, 2007 at 12:00:04 PM EST
[ Parent ]
OK, its the same number of switches, the central access is more space conserving, the two separate flyovers more flexible. Looks like a footprint / cost / frequency tradeoff to me.


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 12:58:02 PM EST
[ Parent ]
... system is unsuitable for the US because the rail slope is different, so equipment that runs on the specialized high speed corridor cannot run on the regular rail system.

He quotes 30% grinding on high speed TGV and 20% grinding on "regular rail around the world" (except for light rail, which is sometimes 0% slope).


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.

by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 01:01:13 PM EST
[ Parent ]
Could you give a link for that comment? It appears that fella' is talking BS, but maybe some details got lost and I'm not familiar enough with North American rail terminology. But assuming it's not my failt, my reply would be:

It is true that US rail and wheel profile is different from the European one, but you solve that by changing both (after all, when the German ICE made a demonstration tour of the US 15 years ago, its wheels were replaced), and it is not a function of high-speed or conventional. (After all, as others said, many French TGVs continue their travel to destinations along conventional lines, say Paris-Bordeaux, which is high-speed less than half-way, only until Tours.)

The grinding rate I know about is a measure of maintenance needs: how much of a line has to be grinded a year to correct rail surface errors. As such it has nothing to do with compatibility with conventional lines. (And on some heavily-used TGV lines, the grinding rate can be not just 30% but up to 50%.)

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Mon Mar 26th, 2007 at 04:15:06 PM EST
[ Parent ]
I can't, its an internal discussion. But the assertion is that the track geometry for the the highest speed TGV's is 30% slope, the track geometry for "regular rail everywhere in the world" is 20% slope, therefore high-speed TGV's are restricted to TGV only track almost exclusively.

Is the distinction between the highest speed corridors and the lower speed corridors track geometry or the actual layout of the track ... curve radius, etc?

My belief is that he has received a garbled interpretation of a poorly understood fact from the middle of one of those pointless arguments between Express Rail and HSR.

However, I had only inferred the opposite from what I had gathered regarding TGV's, and did not know it directly.


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.

by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 04:35:47 PM EST
[ Parent ]
Is the distinction between the highest speed corridors and the lower speed corridors track geometry or the actual layout of the track ... curve radius, etc?

Basically the latter: key factors are minimum curve radius, distance of the two tracks and distance from buildings/walls, switches. But other requirements are: stronger and more tense catenary, special signalling and train control system, and a number of safety measures (like sensors for cars falling off bridges).

To bolster you even further, here is a picture of what someone referred to upthread, a TGV pulled by a diesel on the last leg of the Paris--Les-Sables-d'Olonne journey along a really really conventional track:



*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Mon Mar 26th, 2007 at 05:23:33 PM EST
[ Parent ]
There very few places that have a catenary structure at all, so the HSR would be defining the strength and tension of the catenory for the bulk of the country.

;)


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.

by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 06:41:26 PM EST
[ Parent ]
Thinking about it, one possibility for what he/you may have meant: rail inclination. That is really about slope, rails being tilted inward, and 1:20 is one of the typical values, and the one preferred for high-speed. However, it is not necessary -- for example German lines have 1:40, the other common value in Europe. But what you should tell your commenter is that international trains in Europe often traverse sections alternating between 1:20 and 1:40, in fact it can vary between these values on the same line (say there is fixed track in a tunnel) -- it is no compatibility problem, only the forces and wear are different.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Mon Mar 26th, 2007 at 04:59:42 PM EST
[ Parent ]
He's use 20% and 30% as values, so it can't be inclination, which in percentage slope terms are like 2.5% and 5%.


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 05:03:47 PM EST
[ Parent ]
Re-reading (I often get confused what with being exposed to both technical and non-technical railroading language from three continents), that does appear to be it.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Mon Mar 26th, 2007 at 05:07:33 PM EST
[ Parent ]

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