This train's halt pattern is a very challenging thing for a single WDM3A as it is pretty much close to the locomotive's practical abilities. The schedule can be maintained, but it will result is a lot of stress on the locomotive. Particularly during acceleration ( called notching), the locomotive will have to be notched up aggressively so as to get the required speed quickly. This is detrimental to the locomotive as it will cause a lot of stress on the engine and the traction equipment and can lead to a very high failure rate. And also, if the train loses time anywhere, it will be very difficult to gain back running time as a single ALCO is already pushed to it's limits with all these halts.
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more... Twins on the other hand, can easily handle the train. They will be more energy efficient as well, as the notching will have to be less aggressive now, thereby needing much lesser fuel, with the added advantage of better acceleration. It will just make the operation of this train easier for the crew and the locomotive as well, while giving some scope for a speed up in the future with the same loco links.