I'm not sure:There is WAP7 loco yard at Gomoh only 29 km away from Dhanbad and Howrah has no WAP7 yard still now.When WAP7s travel to Howrah from Gomoh yard it takes Black Diamond or Coal Field from Dhanbad.And it also travels towards Dhanbad with Black Diamond or Coal field because if any major maitainance is neede at Gomoh.If they run without train then money 'll be wasted