Depot driver is different to mainline driving in that you wouldn't be qualified to drive on Network Rail metals. You would be confined to depot limits and passed only in the rules that apply to driving trains in the depot along with the rules, instructions, traction and policies of whichever TOC you are employed by. Assessments and interview are the same as mainline driver as you are still driving trains albeit at 5mph although the training is shorter than mainline driving, around 3-4 months depending on location.