Kiwirail 919 (Christchurch - Invercargill) caught at various spots on its journey from Gore to Invercargill, and features the DX shattering the morning tranquility as it climbs the Kamahi Bank.
Yes there is. The length is dependent on the length of the passing loop as alot of New Zealand is single track, with passing loops where one train can pull into to allow another train to cross. The weight of a train is dependent on the ruling gradient & each class of locomotive has a maximum weight it can haul eg a DX can haul more than a DC. For Southland it is normally around 2000T and 900 metres