Is this construction permissible on any American standard gauge RR?

There is a turnout very close to a broad high-speed curve bearing left. The curve in theory would be superelevated and it it would be an easement curve gradually decreasing radius. Note the switch frog only 18 feet from the point where the straight track begins the curve. Does gradual increasing degree of superelevation (bank, bevel) begin right where the curve begins or along the straight section of track just before the curve begins? My guess is that superelevation would increase gradually as curve gradually decreases radius.

hard to say, if you could get an angle looking towards the curve while the switch is in view, that would be easier to judge, right now it looks a bit tight going to the right

That double switch to the left will give you trouble even in real life. In Trainz it's recommended that you space switches apart and place a spline point before each switch.

-----O---O-------O---O------

O = spline points
---- = track.

Like this shown above. In that case, based on your pic, you can place your junctions on the far left and far right "O"

The only exception for not placing two spline points is when a switch is on a curve, but then you still wouldn't have two switches too close.

Now. TS12 and T:ANE not using the procedural track, pretty much allows for some really, really tight switches and odd combinations that sort of render okay, but this will fail immediately in TRS2019. Protrack especially will throw up red spline points at the junction, and will also complain about non-procedural track being too tight as well.

The other thing too to consider is rendering. I have found even in TS12 and below, is that if a radius is too tight, the track looks awful and engines can't always pull through the switches due to the tight radii.

You may not be using T:ANE and up or procedural track at the moment, but always plan for the future so stuff doesn't have to be redone.

Since there needs to be a straightened piece of track leading the the facing side of the switch, and two straightened sections should not be directed connected without a non-straightened section between them, I have found that two turnouts can be back to back without an intervening spline point, or else two spline points need to be used. A single spline would have two straightened sections joined. Unless the angle between the two sections is exactly 180 degrees, this will cause a discontinuity, no matter how slight.

- non straightened
= straightened
o spline point
< left to right, a diverging turnout

>o=o<
or
>o=o-o=o<

but not

>o=o=o<

martinvk said:

Since there needs to be a straightened piece of track leading the the facing side of the switch, and two straightened sections should not be directed connected without a non-straightened section between them, I have found that two turnouts can be back to back without an intervening spline point, or else two spline points need to be used. A single spline would have two straightened sections joined. Unless the angle between the two sections is exactly 180 degrees, this will cause a discontinuity, no matter how slight.

- non straightened
= straightened
o spline point
< left to right, a diverging turnout

>o=o<
or
>o=o-o=o<

but not

>o=o=o<

Click to expand...

The Trainz game itself has no issue with my switch installation as shown. Both switches back to back are on a straight section of track which is the mainline. Both switches lead to sidings off the mainline. The mainline is high speed, not the two sidings. That broad bend to the left is the mainline still. That bend to the right is a slow siding off the mainline. I'm just wondering if actual American roads might employ such a switch siding configuration close to a mainline curve on a 50 MPH mainline. The short track section between the switch points is actually straight as an arrow. No part of any switch including frogs is actually on the curve part of the mainline.

I've seen this on branch lines where there's various industries that need switching. There are usually two locomotives, one on each end, to switch either direction. Generally on mainlines, switches set like they are can get picked causing derailments and sidings that require pulling into are not used much anymore. The trailing point sidings are the easiest for the crews to switch since they can back in, grab, and go.

This is a large G-scale Modelz Trainz layout of about 13 scale miles for the longest loop on the layout. Siding 2 pictured above leads to Thompson's Sawmill to make log/lumber pickup/deliveries. Siding 1 bypasses the large staging yard of the route (layout). This allows the local district road switchers to make their appointed rounds to its local rail freight customers without having to drive through the staging area in a long, roundabout fashion. The mainline is a long loop that goes through the back staging area while the local RR district tracks is a short loop, the main focus of the layout. The main lines going to and from back staging area (fiddle yard) simulates railroading beyond the local district. It acts somewhat like a portal where mainline trains, under AI operation, are held and time-released to make a periodic run about the local district loop for added realism. Passenger mainline trains stop at the district passenger station. Mainline (perhaps divisional) locomotives parked back in the staging area periodically pick up freight rolling stock from the district yard and return cars there and banish picked-up cars to the staging area. The local yard serves the customers of the district and has its own roundhouse. Railroads are broken into districts, sections, divisions, subdivisions, mainlines, branch lines and so forth.