I saw this meme on Facebook showing a coiled railway overbridge and an alternative plan. I replied that straightening that overbridge will force it to start at the other side of the road, and you need to build a u-turn and there is a valuable building off the frame. Is the coil rational, and why?

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2 Answers 2


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The distance between the intersection and the rail is 100m, The road would need to rise about 10m to clear the track. This would mean a average grade of 10%. However you also need to account for the vertical curve in the road so the max grade would be quite a bit higher.

The max grade allowed for non-local roads in the US is about 8% (the place in question is in Pakistan). This appears to be a connecting road that replaces a on-grade railway crossing a bit further east.

With this design you also have a lot more span that you can cross under next to the rails for future development.

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    $\begingroup$ And to probably help reduce the speed of approach to the junction... $\endgroup$
    – Solar Mike
    Oct 31, 2018 at 11:29
  • $\begingroup$ Could you also answer why they didn't use an extended straight ramp but with a legal grade? $\endgroup$ Oct 31, 2018 at 11:44
  • $\begingroup$ @aitchnyu extended to where? because that would not physically fit, which would result in either the trains crashing into the span or a lip at the intersection. $\endgroup$ Oct 31, 2018 at 12:10
  • $\begingroup$ Rachet is saying you need the extra length of road to get to the height required to pass over top rail tracks safely. A tighter loop probably could have been used, but it looks like they are circling a storm water management pond or the like. $\endgroup$
    – Forward Ed
    Oct 31, 2018 at 14:13
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    $\begingroup$ I believe @aitchnyu meant, when going North, having a right turn uphill parallel to the railway followed by a left turn over the railway and finally a slight right turn on the other side to align and quit on the north-east. However, this would not add much available slope length when considering possible widening of the railway. $\endgroup$
    – yo'
    Oct 31, 2018 at 15:24

In 1909, the same thing was done twice on the Canadian Pacific Railway rail line through Kicking Horse Pass in the Rocky Mountains: Spiral tunnels at Kicking Horse Pass

Two circular tunnels (dashed white lines) were dug into the mountains, lengthening the route in order to decrease its steepness.

This is exactly the same situation and solution as in the original question.


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