Chris Walker Wrote:
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> Yes Brian, the road I live on is indeed 1 chain
> wide, and there is even an Australian country song
> about the 3 chain road (Lee Kernaghan - Three
> Chain Road ).
> The reason I asked just how many degrees was a 7.5
> chain curve was that is the tightest on the
> Raurimu Spiral and requires a 45 Km/h speed to
> traverse. I've often wondered just where that fit
> in with your systems such as the D&RG? A 20°
> should then be 4.3 Chains.
7.5 chains is 495 feet. Satellite imagery of the Raurimu Spiral indicates curves with an overall diameter of very nearly 1000 feet, matching very well with the 7.5 chains figure. In american parlance that'd represent curves in the vicinity of 11.5 degrees. 20 degree curves are, as you say, about 4.3 chains radius and 30 degree curves are in the vicinity of 2.9 chains. In addition to degrees, american practice often referred to curvature by its radius in feet (particularly in the early days), more directly comparable to Commonwealth practice.
For the most part, NZR built to good standards for its day, but it took a long time to do it. I imagine it wasn't cheap. In the Australian state of Tasmania (its railway is 3 foot 6 gauge), some of the branch lines used 3 chain curves (29 degrees or therabout), as most of that state's rail lines were built with significant cost limitations. The main lines were broader, with 5 chain curves originally. The opinion of the time was that using 6 chain curves instead would've doubled the cost in those areas.
I don't know how NZR decided upon its speed limits. At different times in U.S. history, railroad speed limits have been based on everything from complex formulas factoring in superelevation and equipment cant deficiency (modern FRA practice) to simply whatever speed would allow the train to pass without tippping over (the early days) and everything in-between.
