The original system of using the Blue Star multiple working was later revived after privatisation as a way of allowing locomotive-hauled stock to replace multiple units on certain routes, thus increasing capacity without the complications of having to run around or drag a dead locomotive at the rear. It was used by First North Western and Wessex Trains with Class 31s, and by Abellio Greater Anglia, Arriva Trains Northern, Northern Rail and Northern with Class 37s all with Mark 2 carriages. The same system was also adopted by Network Rail for its track observation trains, although on many trains one locomotive has recently been replaced by a DBSO modified to work with Blue Star.