Effectively you're going into a 3.0 metre by 3.6 metre box, so no problem eh?
Yeah it's wide enough for a legal New Zealand caravan or motorhome (2.55m wide max) with about 5 inches old measure each side.
And it could be a very tight fit for a full height legal motorhome (4.3m max). Pretty certain a bus or truck won't fit due to its height.
So no problem, eh? Yeah right!
This is just an interesting part of the New Zealand roading network, which made me wonder, "Why so skinny?"
The geocache is on the other side of the box from State Highway 1, so consider carefully how you approach it.
There is a turnaround and parking space next to GZ, but very limited (read None) parking on the SH1 side.
By accepting the desire to attempt this geocache, you (the finder) absolve Phronimos, (the hider) of any consequences of your underestimating the dimensions of your chariot.