The designation DXB denotes that the locomotive has been fitted with the Brightstar electronic traction control system, while DXC denotes that the locomotive has been additionally fitted with modified air intakes ("chutes") as well as all the other upgrades including Brightstar. Thirteen of the original batch of 15 have been upgraded to DXB standard (DXC 5039 and DXC 5520 (née 5045) being the exceptions), and most of those from the subsequent batches upgraded to DXC standard - exceptions being DX 2639 (long since withdrawn from service).