Extension rods can be made from .061 wire and switch motors mounted completely under the layout. Or the remote mounting kit could posibly be used. Or you could put servo motors in the stonework.
I’ve never seen any specific guidelines for the prototype railroads. As someone noted, a turnout is a likely place for a derailment, so a railroad if possible would want to allow enough room (if possible) that a derailment didn’t involve the tunnel or bridge. I would say on a model railroad, where say two tracks come together to go over a bridge or through a tunnel, I’d leave about one car length (40-60’) clear.
BTW note that in the photo earlier of two tracks coming together to cross a small bridge, it’s actually a ‘gantlet’ - the two lines aren’t coming together with turnouts.
I’d like to find out where this is. The gantlet is what first caught my eye, but I think Gregc was pointing out the turn out, just before the bridge, on the left.
I checked out the Bellows Falls thing, looks close, but I don’t see the gantlet.