Rail track alignment design

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In a discussion of the impact of the UK's HS2 high speed rail project on ancient woodlands, Gareth Dennis discussed the design of rail track routes taking into account constraints of track radius and "cant" for different running speeds on possible routing of a line.[1]

P-way video fun-times!

This time, I'm looking at the process of track alignment design (or more specifically RE-design)...

I'm going to cover:

  • the survey information we collect
  • how we then use that data in 3d
  • creating the horizontal/vertical alignments

Here is last week's video session on curvature:

There's been a lot of curvy chatter on here this evening, so I thought I'd finally do a thing I've been meaning to for a while... Compare curves/speeds/destruction!

So let's zoom out and take a look... When I say "maximum cant", I mean 150mm of applied cant, which is the normal maximum on the GB rail network.

What do I mean by cant?

In the case of normal railways, this means lifting one rail above the other to balance the inwards and outwards forces generated as a train passes through a curve.

Cant is also called "superelevation" so we abbreviate it as "E" and calculate it thus:

Track geometry - curves - Gareth Dennis.jpeg

Zooming out even further, we can look at maximum curvatures/minimum radii for some higher speeds (and hear me say "kibosh" a half-dozen times):

Alignment designers use "speed tables" to quickly assess the capability of a train to negotiate a sequence of curves at the proposed permissible speed...

Here's one I've bodged to calculate the curvatures for all of the colourful curves in the video:

Speed table - Gareth Dennis.png

Now we're really picking up speed... Here are some curvatures for high speed lines like HS2 or some of the really super high-speed lines in China:

Lastly, let's hop (willingly or otherwise) into a #Loopyhype tube for the ride of our lives!

Anyway, I hope that was interesting enough... As ever, let me know if you think of something interesting you'd like me to try and visualise in a way that makes sense!

In the meantime, you can download that @GoogleEarth KML here

p.s. here is the next slide in my lecture on the subject, in case you are interested in what limits cant or cant "deficiency" (which is really a measure of how much lateral force you decide NOT to balance out with cant):

Cant 3 - Gareth Dennis.jpeg

p.p.s. for the real Bahnnerds, here are the standards that define how we apply cant (the TSIs are more relaxed, NR are more stringent):

Cant 2 - Gareth Dennis.jpeg
Cant 3 - Gareth Dennis.jpeg

Footnotes and references