Under Section 11 of the Road Traffic Rules - Vehicle Standards and Compliance, what is the minimum tread depth a tyre on a motor vehicle must have in Papua New Guinea?

1. 1.5 mm in all principal grooves containing moulded tread depth indicators, around the entire circumference
2. 1.6 mm across the central three-quarters of the tread width only
3. 3.0 mm anywhere on the tyre
4. Tread depth is not regulated; only visible cords are an offence