[1] The Dash 9-40CW was basically an extension of the previous order for the standard cab GE Dash 9-40C, built under the same premise that a lower power rating would prolong the life of the engine and use less fuel.

In 2005, GE replaced the C40-9W in its locomotive catalog with the Evolution Series model, the ES40DC.

Like the Dash 9-40CWs, Norfolk Southern's ES40DC locomotives are rated at 4,000 hp (3,000 kW) to conserve fuel.

The change in output is accomplished electronically; mechanically, the two models are essentially the same.

Unlike the North American axle load limit of 71,500 lb (32.4 tonnes) on standard gauge railways, the narrow gauge railway over which the units operate allows only 51190 lb (25 tonnes).