Atlas N Scale #54031 ALCO C-628 diesel locomotive, Delaware & Hudson #611, in the classic D&H gray, blue and yellow “lightning stripe” scheme with the shield herald on the cab.
This is from Atlas’s original C-628 release (the 54000-series), which introduced the model in 2004 with a split-frame mechanism, blackened low-profile wheels, LED lighting and AccuMate couplers. It is a standard DC model (DCC-ready, no decoder installed).