Third Rail Dimensions

For the CTA specifically, and maybe more generally for other systems, what is the offset for third rail from the track center as well as top of the standard rail?

I can't seem to find anything definitive.

The most recent (!) definitive data on third-rail dimensions and placement that I know of is the A.E.R.E.A. standard given in the _Electric Railway Handbook_, by Albert S. Richey, McGraw-Hill, 1915, pp. 673-675. The whole book is freely available online at https://archive.org/details/electricrailway02greegoog.

I know, it seems weird to refer to a standard more than a century old, but remember that the vast majority of third-rail installations in the US (including Chicago's) really are that old, and—except for things like BART, which don't interoperate with anything at all—there's an unbroken chain of backwards compatibility from 1915 to now. You can't change those dimensions without changing all your equipment, which is painful enough that you'd need a really good reason. Honestly, I doubt that the CTA has changed its loading gauge since 1915 (that would require changing all the platforms), so why move the third rail?

Thanks, that's a keeper. London Transport has a spacing of 350mm, which is 13.78" and matches the drawing you referenced if I'm reading it correctly.

Screenshots are from one of the modeling projects I've been working on for OpenRails - a short segment of the Oak Park line that runs on the CNW right of way, as well as the shops at the end of that line.

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There was a lot of Chicago influence on the London Transport system - on some lines trains are made up of "cars" and not "carriages", and the Hedley truck was used on Lake Street and London Transport equipment.

I'm just barely old enough to remember the Lake Street L running in South Boulevard next to the C&NW in Oak Park and Chicago (on overhead wire west of Laramie). CERA bulletins B-113 and B-115 cover lots of technical info, including track maps.

It was more than just a lot of Chicago influence in London. The same man Charles Tyson Yerkes built both systems. Chicago first in the 1890s and London in the 1900s. Yerkes was kind of a scoundrel but he created unified systems versus other cities where each line was individually developed without regard to ever being able to connect to each other.