Roll Over protection devices are legal in WA, see construction and installation guidelines
here
My understanding is that the two main concerns with ROPD are passenger and pedestrian safety.
The former is concerned with potentially intervening objects in passenger headspace (i.e. for internal roll cages) in collision situations. The latter is concerned with pedestrian safety. I've discussed the latter with 2 different DPI tech staff, both confirming that so long as the ROPD doesn't "significantly" protrude outside the vehicle envelope, it is deemed OK. Which they agree, for a Deefer, is not an issue. For a disco?? - I'd confirm it with the DPI prior to sinking the dosh for a cage.
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