Complex sentence: There are 1390 public road level crossings in New Zealand, of which 275 crossings are protected by flashing red lights, bells, and half-arm barriers; and 421 are protected by flashing red lights and bells only.
Split into simpler sentences: There are 1390 public road level crossings in New Zealand. Of those, 275 crossings are protected by flashing red lights, bells and half-arm barriers, and 421 are protected by flashing red lights and bells only.