In Spain they have variable-gauge trains. The train is driven slowly across the junction; each bogie has various projections that are engaged by control rails t

In Spain they have variable-gauge trains. The train is driven slowly across the junction; each bogie has various projections that are engaged by control rails to take the weight off the wheels, unlock the wheels, slide them to the new gauge, and lock them in place again. Pretty surprising. Has been in service since 1969.