The GE Dash 9-40CW is a road switcher diesel-electric locomotive built by GE Transportation Systems of Erie, Pennsylvania, between January 1996 and December 2004. 1,090 were built for Norfolk Southern Railway, as road numbers 8889 to 9978. 53 GE Dash 8-44CWs built to Dash 9 specifications were also built for CSX Transportation, carrying road numbers 9000 to 9052. Part of GE's "Dash 9" series of locomotives, the Dash 9-40CW shares its frame, HiAd trucks, 16-cylinder 7FDL engine, and 752AH-31 traction motors with the GE Dash 9-44CW. But while the more common 9-44CW offers, software in the 9-40CW's engine-governing unit restricts its power output to, although the engineer can override this restriction when desired. The Dash 9-40CW was basically an extension of the previous order for the standard cabGE Dash 9-40C, built under the same premise that a lower power rating would prolong the life of the engine and use less fuel. Early production units built for CSX were designed with carbodies externally identical to the predecessor Dash 8-40CW with the first three units of the series also being built on Dash 8-40CW frames, and were designated C44-8W originally, as they were built as 4400 horsepower units before being downgraded to 4000 horsepower. The CSX units were equipped with GSC Floating Bolster 3 Trucks instead of the standard Hi-ad trucks commonly found on later models. In 2005, GE replaced the C40-9W in its locomotive catalog with the Evolution Seriesmodel, the ES40DC. Like the Dash 9-40CWs, Norfolk Southern's ES40DC locomotives are rated at to conserve fuel. The change in output is accomplished electronically; mechanically, the two models are essentially the same. In late 2013, NS started to upgrade their C40-9Ws into C44-9Ws by increasing the wattage from, thus increasing the horsepower rating to. The locomotives were upgraded as they went in for their 184-day maintenance cycle. The upgrades were completed by 2015. In 2017, NS started to rebuild its older Dash 9-40CWs to AC44C6Ms, with the same rebuilding procedures as the standard cab Dash 9-40Cs. All of the Dash 9s on the roster are expected to be rebuilt to AC44C6Ms by 2027, with the first 400 to be completed by 2022.
