Should we change the Virtual Transition length?

A different kind of article … Antescript Several times, in the last ten years, I started to write articles with this title. The only draft I kept is so convoluted and confusing that I might even decide to publish it. I have a few answers to this question. There is one I hesitate to put…

When is the cant negative in LandXML?

Motto: “I don’t see the code anymore. All I see is blonde, brunette, redhead, negative, adverse.” Cypher Disclaimer: This is not a design guidance. Don’t believe everything you read online. LandXML? LandXML is a non-proprietary data standard on the Extensible Markup Language (XML) format, developed for engineering data exchange. A LandXML file can contain civil and survey…

The other Bernoulli boy and his lemniscate

When I hear the name Bernoulli I think about some funny high school experiments of spraying coloured water on paper but also about an infinite loop curve the Roads Professor tormented us in Uni. I would have bet both things were discovered by the same Bernoulli. But no. The more known one, D. Bernoulli, the…

Hallade’s broken clothoid

I mentioned in a previous article, The Cubic Parabola – a complicated simplification, that the curvature diagram of the Cubic Parabola increases linearly up to a peak point and then drops down. Only that first section of the parabolic curve can be used as an alignment transition. The curvature diagram of the Clothoid is however…

The equivalent radius (versine bending)

Prologue One of the main giants on whose shoulders stood proudly Isaac Newton, is the French mathematician Renatus Cartesius. He was the first to label the unknowns in equations by the letters X and Y and also he defined the annotation of powers as superscripted labels X2 . Believe it or not, that was a…

The Cubic Parabola – a complicated simplification

Ten years ago, one of my first British friends asked me “Why 4°?” The Clothoid is by far the most used transition curve for railway and highway alignment design. I wrote about this marvelous curve in an old article on this blog – here. Although the Clothoid is the ideal transition for linear variation of…

Straightening the equivalent radius

If we consider a circular curve of radius R2, tangent to a straight and mark the offsets O1, O2 and O3, measured perpendicular from the circle to the straight and placed at regular C/2 interval we will get something like this: The offsets O1 and O3 are the bases of a trapezoid and O2+V2 is…

Where’s the point?

All the railway networks have design rules for marking the limit from which it is safe to stable a vehicle on a line, without the risk of obstructing the train passage on the other line of an S&C (turnout or whatever other arrangement). In the UK this limit comes in a pair – Fouling Point…

What’s the degree of curvature?

… or – How to convert a curve into an angle? In the track design handbook we have a too complex formula that refers to “degree of curvature”. Before discussing about the equivalent gradient, let’s see first what this is – what is the degree of curvature? This measure is used in United States in…

Which is better – S&C or plain line?

Thank you for visiting this page. I would really appreciate if you could spare a minute and answer the few questions below. I’ll publish the responses with a few comments as soon as enough answers are collected. If you don’t see the form below, please go to this link: Which is better – S&C or…

Cant deficiency converted in percentage of g

As demonstrated in a previous post here: https://pwayblog.com/2015/10/29/11-82_cant-deficiency-un-compensated-acceleration-pway/ , the cant deficiency is the conventional representation of the uncompensated lateral acceleration. And since cant deficiency is an acceleration, we can easily represent it as a percentage of g, the gravitational acceleration. The formula that relates the cant deficiency D to un-compensated lateral acceleration is: The…

Is the surveyed cant the actual cant?

One of the instruments used to survey the track is the rail shoe – an L shaped device placed horizontally on the rail head, that touches laterally the running edge at 14mm below its horizontal arm – see figure 1. The horizontal placement of the shoe is checked using a spirit level. There might be…

Versine artefacts?

Motto: If you can’t explain it simply, you don’t understand it well enough. (Easy for you to say…) Einstein Well, hello again, dear reader! Before moving on from the TGSD Calculator allow me to explain what it measures, without any reference to waves and filters, without frustration or passive-aggressiveness (is that an actual word?) ,…