Complex sentence: This means one train doing the work of sixty nine 44 tonne lorries in the UK and the rest of the world, but on aggregates trains the Class 60 will do the work of 120 lorries.
Split into simpler sentences: This means one train doing the work of sixty nine 44 tonne lorries in the UK and the rest of the world. But on aggregates trains the class 60 will do the work of 120 lorries.