On the British railways the men who run the trains are safeguarded very efficiently, and the collisions and derailments which are serious enough to do injury to the trainmen or the enginemen are really rare.
The design combines ample boiler capacity with large adhesive weight and moderate axle loads, but except on heavy gradients or for unusually large trains requiring engines of great adhesion, passenger traffic can be more efficiently and economically handled by four-coupled locomotives of the eight-wheel or Atlantic types.
The wing to act efficiently must be driven at a certain speed, and in such a manner that the down and up strokes shall glide into each other.