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My guess is that it will reduce track friction considerably while avoiding derailment.

Explanation : To make sure wheels stay on track, wheels have rims, which brush against the track from sides.These rims introduce friction in addition to rolling resistance of wheel. This idea tries to avoid that problem. Idea is to have wheels without rims/flanges with flat edges. Track will also be flat at top. But then to make sure train does not derail, i.e. stays on rails, add wheels on sides of rail. These wheels will be parallel to ground and roll on rail from sides. Both sidewheels will either be inside of rails or outside. This will avoid derailment.

Rollercoasters always use side wheels in addition to regular wheels. They don't use flanged wheels like regular railway.

 — VJW, Dec 04 2010

Baked on monorails and guided bus systems.
 — pocmloc, Dec 04 2010

 This is entirely clear.

Oh, wait - this is entirely unclear.
 — MaxwellBuchanan, Dec 04 2010

 What [pocmloc] said.

 This causes problems at some types of points (switches).

[MB] do try to keep up ...
 — 8th of 7, Dec 04 2010

This, I think, is a modification to another idea, to which it should at least have reciprocal links - if not replaced entirely by an edit to the other idea.
 — lurch, Dec 04 2010

 I think I got it:

 Train wheels with a second wheel running inside the rail instead of the main wheel having a flange, the purpose being to eliminate friction due to the differential rotational speed of the wheel andrim.

In practice, however, there is essentially no such friction, because the wheel is stationary with respect to the rail at the point of contact, and nearly so at all points the flange can contact the rail.
 — MechE, Dec 05 2010

The flange does not touch the rail in normal straight line running. The rail head is slightly domed, and the wheel rim slightly angled, so the wheelset 'floats' centrally on the rails. The flanges are merely to catch any sideways drift.
 — pocmloc, Dec 05 2010

//The flanges are merely to catch any sideways drift// Is that the cause of the intermittent squealing sound made by trains?
 — spidermother, Dec 05 2010

 No, that noise comes from passengers who've just been told the price of a return ticket by the conductor.

 Wheel noise may arise from several causes:

 Railway axles are rigid and coupled; there is no differential movement, unlike a road vehicle. Therefore, when cornering at low speeds, one wheel is obliged to "slip". This can be the inside or outside wheel.

Flange contact at curves or points also causes squeal. This is noticeable when a train traverses a cambered curve intended for high speed running at a lower than normal speed; the axles tend to hunt down toward the inside rail, causing flange contact.
 — 8th of 7, Dec 05 2010

//Flange contact at curves or points also causes squeal// I recommend you apply flange ointment twice a day to the affected area.
 — pocmloc, Dec 05 2010

//Railway axles are rigid...causing flange contact// [+] because I learned something from the anno thread which I enjoy knowing.
 — mouseposture, Dec 05 2010

Rail wheels do not slip, despite the solid axle. As previously mentioned, the contact surface of the wheel is slaghtly angled, so the wheel is in fact conical, with a larger rolling diameter at the inside, smaller at the outside. As the axle comes to a curve in the track, it initially continues in a straight line, so the inner, larger diameter of the wheel on the outside of the turn is on the rail head, while the outer, smaller diameter of the wheel on the inside of the turn is on it's rail head. The difference in rolling diameters allows the axle to negotiate the turn without slipping.
 — Twizz, Dec 06 2010

So there's feedback between the steering angle of the wheelsets and the lateral position on the tracks, keeping everything lined up, whether the track is straight or curved? That's genius! How did I only just learn that?
 — spidermother, Dec 06 2010

[Twizz], you are correct - when the wheel is moving fast. But at very low speeds (shunting, approaching /leaving a station) some stick/slip does occur as the dynamic forces inducing the wheel to "centre" are very much reduced compared to the static load.
 — 8th of 7, Dec 06 2010

Even at low speeds, an axle on it's own will follow the track. The flanges only come into play where the turn radius is tighter than the tread angle can accomodate. This is often the case where there are points and in shunting yards.
 — Twizz, Dec 06 2010

..... which was the essence of the explanation.
 — 8th of 7, Dec 06 2010

if you have ever looked closely at a used freight train wheel you would realize that the sides almost never touch the rail. This is simply a non problem.
 — WcW, Dec 06 2010

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