>>1768602>Then why do they use SD70s with twice the tractive effort of an SD40 now?They're still single-engine units. If one of the prime movers on a DD40 went down, in essence both would go down because the whole unit would have to be taken out of service when it went into the shop for repair. If it was two GP40s (which is what a DD40 is), then the working unit could still be on the main line making money. That's why these big diesels never caught on, the flexibility of smaller individual units is more economical.
