prevent the mainline from fouling if there is no place for a derailer

[bigdawgks]

Agree with the post above. When correctly operated the turnout you circled in yellow should provide the same protection for the mainline. A derail there would be superfluous.

If your hypothetical derail were manually operated, then manually setting the switch to protect the main could replace that procedure. If your derail was intended to be operated by interlocking then you might have a case that the manual switch wouldn't provide the equivalent protection.

[chuck geiger]

Be still, my beating heart, is this the Mojave? which I am doing as well. Or Edison? (which I just saw it might be).

[Hazuki]

Thanks for the inputs.

@chuck geiger: It's freelanced but inspired by the mojave scenery.