Weird question of the day

The New Haven rr tried it in the 19th century ,the results were not good... 

They tried, too dangerous.

Rusty

This article doesn't say why one rail placement was favored over the other one, but it does include some modern uses of a central third rail:

https://en.wikipedia.org/wiki/Third_rail

Tomlinson Run Railroad 

Maintenance.

The sliding power pick-up shoe is a wear item. It is much easier to replace an external shoe positioned to the side of the locomotive than it is to have to spot the engine over a pit to replace it from underneath.

There is also no way to shield the center rail to protect passersby from electrocuting themselves should they happen to touch it.

I would think an outside outside power rail also means much less complicated track work at switches than a central rail, since you don't have to worry about shorting across a running rail that carries the return current.

The London Underground uses a four-rail system (with both the positive and negative power rails set higher than the running rails) in order to isolate traction current completely from the running rails for a variety of technical reasons, but it's clearly more expensive to build and maintain and the complexity of switches is greatly increased.

Here's a link to information about the Tube, including an explanation of the 4-rail system:  http://www.trainweb.org/tubeprune/tractioncurr.htm

I think Rich hit the nail on the head, the maintainence of the pickup equipment under the units would be more difficult than with an outside third rail. Safety wise they could potentially have built the third rail into a trough of sorts, similar to what they did with streetcars in Manhattan and the Bronx where overhead wire was not practical or banned, but I think the maintainence would likely be the primary reason for not doing the inside third rail.  Good thoughts all!

A third rail in a trough sounds pretty complicated.  Wouldn't the contact shoe have to be raised out of the trough at switches so as to cross above the running rail, rather like the grip had to be raised on SF cable cars in order to cross an intersecting cable line?

Oh, yeah.  Here what a grade crossing looked like:

Looks like the third rail was insulated near the timbers, but can you imagine the jolt if someone tripped or slipped, fell and touched the third rail?

And the contact would then have to grind it's way across the timbers.

Rusty