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The Big Boys were the only locomotives to have the 4-8-8-4 wheel arrangement, combining two sets of eight driving wheels with both a four-wheel leading truck for stability entering curves and a four-wheel trailing truck to support the large firebox.

The Big Boys were specifically designed to pull a 3,600 short ton freight train over the long 1.14% grade of the Wasatch Mountains in Utah.

Before their arrival, helpers were needed. Adding and removing helpers from a train slowed them down. For such locomotives to be worthwhile, they had to be faster and more powerful than slow mountain luggers like the earlier compound 2-8-8-2s that Union Pacific ("UP") tried after World War I.

To avoid locomotive changes, the new class would need to pull long trains at sustained speed (60 mph) once past the mountain grades. Towards the end of the 4000's career (in the late 1950s) it was found that they could still pull more than their rated tonnage of 3,600 tons. Their ratings were increased several times until they regularly pulled 4,450 short tons up the Wasatch grade, unassisted.

Billionaire Benefactor - Career System scenario

You take control of a restored Big Boy on its first passenger service. A billionaire railroad fan has donated millions to get this Big Boy running on the main line for passenger specials, and you are taking control for its debut run.

You have speed and time targets to reach, so as not to disappoint the many photographers who have turned out for this momentous run to Barstow, as well as a trainload of excited passengers.

Monument Free Roam

Choose a Big Boy and click on it to drive it

Cajon Free Roam

Choose a Big Boy and click on it to drive it

Routes Featuring the 4-8-8-4 ‘Big Boy’Bath Green Park to Barstow