Is a zig-zag permitted on any American standard gauge mainline?

[JonMyrlennBailey]

This is an S curve. A right turn immediately followed by a left turn, vice-versa, with little or no straight section of track between opposing turns.

 

[DWBennett55]

This is an S curve. A right turn immediately followed by a left turn, vice-versa, with little or no straight section of track between opposing turns.

Not according to UP specifications. For main line and branch lines, the minimum straight track segment from the end of one curve to the start of an oppisite curve is dependent on the maximum track speed. For 60 mph and above the minimum tangent distance is 500 feet. For 40-59 mph, the minimum distance is 300 feet. For 39 mph and below the minimum is 150 feet. For yard and industry tracks the minimum is based on the degree of curve: 7°30' or less, 36 feet and for greater than 7°30' the minimum is 60 feet.

All the above from from Union Pacific's site: https://www.up.com/customers/ind-dev/operations/specs/track/index.htm

Lots of very good info there that I've used when making my assets and in surveyor.

Take care,

 

[JonMyrlennBailey]

I have a straight section between my opposite curves on the mainline in a 25 mph zone. It is about 1/2 locomotive in length. It seems awkward. While riding in the cab as soon as the engine clears one curve its seems to immediately start the opposite curve. I am going to have to redo my model layout and put more tangent in where it would seem natural. Having these sudden shifting curves may make passengers on the train sick. On a physical layout I would have well-engineered easement curves as well but this is difficult to do in Trainz Surveyor.

 

[cascaderailroad]

Having these sudden shifting curves may make passengers on the train sick

Virtual Trainz passengers do not get "train sick", as Trainz is just a cartoon simulated video game ... nothing more ... drive more slowly, manually, in the cab

 

[pware]

The term "Zig-Zag" does not refer to an "S curve". It is used in the UK/AU/NZ railroading world to mean what you Americans call a "switchback".

 

[JonMyrlennBailey]

I got that term zig-zag from the Olympic bobsledding course. Pardon. This goes back to Lake Placid, NY in 1980.
What the Olympic Winter Games sportscaster called a zig-zag on TV looked like an S curve to me.
Talk about nausea on such abrupt curve changes at bobsledding speeds!


Anyway, I just corrected the short straight track sections between my opposing curves by making these sections longer as DW suggested above IAW UP standards. Not too much work.
Likewise, I don't have excessively short straight sections (tangents, segments??) between two curves turning the same direction as well as this is also aesthetically not pleasing.
The only exceptions to not having very short straight sections between two curves is for crossovers between two mainline tracks, customer sidings and perhaps in my yard where trains go pathetically slow, 10 mph, anyway. At these low speeds there is nothing dramatic in having such short tangents as trains creep past them. It won't cause me any nausea. I know from my experience with S curves on HO layouts years ago cars would come uncoupled as they would weave through an S curve with no tangent so this can be a mechanical issue in physical model RRing.

 

[cascaderailroad]

in my yard where trains go pathetically slow, 10 mph, anyway. At these low speeds there is nothing dramatic in having such short tangents as trains creep past them. It won't cause me any nausea.

That is were the fun is ... I like driving JR noisy gons, and making super slow switching maneuvers at 1 to 5 mph ... if a prototype RR shoved railcars in at AI speeds of 35 mph, breakneck speeds, there would be a derailment each and every time