difference between 168/1 and 2s and 170s and 171s

[Cherry_Picker]

Cough. 170's are approx. 20% heavier

20% heavier than what? I mean there can be significant weight differences between subclasses, a 168/2 is quite a bit heavier than a 168/0 for example.

The difference in track access charge could be down to something as silly as a different price was negotiated.