Fig 1
Searching I found a reference to 15" minimum radius for 4-8-8-4 Big Boy,
which has two drive axles on each articulated section. Another reference gave
worst case over 22", most equipment 19". A 3 drive axle nonarticulated steam
locomotive would be amongst the worst.
On straight track
On curves minimum radius and track to track spacing
intersection A n B ∩
