In the days of mechanical signalling, and before power operated points existed, was it possible for one signal box placed in the middle of the triangle to control the points at all three junctions? Or was the distance too great for the strength of the average signaller? If yes, do you know of any examples?
Arundel Jn, Minster and Bradford(-on-Avon) Jn come to mind.
From the SRS site, Arundel Jn had one motor-worked point at the Littlehampton end (its "pair" being self-acting); Minster looks to have had the same at the South junction - both were SR rationalisation.
The "new" Bradford Jn box (already mentioned) was cunningly sited halfway between the
West North and South junctions, and I imagine the rodding to
North West ran direct from the box, at right angles to the rest, so could well qualify.
EDIT: got disorientated - see
Gloster's post later
Severn Tunnel Junction at Salop?
Severn Bridge Jn doesn't actually control all the triangle - and even the junction at Abbey Foregate looks to have been added to its layout as a "modern" rationalisation - I would hazard a guess that the points are motorised (Tim Dunn, are you on here?!).
As
John Webb has said, the vast majority of triangles needed 3 boxes.