Traffic islands are defined in Section 1.6 of the Land Transport (Road User) Rule 2004 as a

a defined area within a roadway, which may be flush with the roadway or raised, and from which vehicular traffic is intended to be excluded.

Localised hazards in the roadway (including, but not limited to bridge abutments, trees, tree pits, swales, and / or other street furniture) should be treated as traffic islands. Where a traffic island is intended to separate opposing traffic, it is a median island.

A median is defined in clause 1.6 of the Land Transport (Road User) Rule 2004

a strip of land that may be part of a road and that separates vehicles travelling in opposite directions

and where traffic is intended to be excluded from a median (including where a road safety barrier is installed in a median), the median is forms a median island.